Monday, June 06, 2016
The week ahead.. cool start with a hot and stormy finish
The weather in southern Manitoba this week will see a transition from a cool fall-like start to a more summerlike pattern by the end of the week, complete with increasing heat and humidity as well as the risk of potentially severe thunderstorms by Thursday or Friday. Highs today will only top out around 19C, some 5C below normal for early June, but by Friday, Winnipeg and the RRV could be looking at temperatures close to 30C. The increasing heat and humidity along with a couple of weather systems tracking across southern Manitoba will lead to the development of scattered thunderstorms, some of which may be severe. Stay tuned through the week as this developing weather situation evolves.
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Yikes, models hinting at a severe bow echo moving through Winnipeg Thursday night.
ReplyDeleteYeah, Thursday night appears to be the main thunderstorm threat period over southern MB. Storms likely to initiate over SE SK/SW MB late Thursday then spread quickly eastward into southern MB Thursday evening/night. Discrete supercells developing initially will pose severe hail/possible tornado threat with storms likely evolving into an MCS/linear type system with strong wind gusts as the main threat across rest of southern MB/RRV Thursday night.
DeleteBy the way, you'll notice currently there is NO mention of thunderstorms in the forecast for Thursday night (only a chance of showers). This is an automated forecast that does not include thunderstorm risks after 48 hours. That will likely change by this afternoon's forecast when human forecasters can add the thunderstorm threat within that time period.
DeleteBy the way, I noticed that EC has started to include "humidex" values in the regular forecast. Not sure what the criteria is to include it, but it appears to be if the maximum temperature is at least 25C, and the humidex is 27C or more (not positive about that) I only wish they restricted inclusion of humidex if it was a certain threshold (say at least 3C) above the forecast high temperature. Saying a high of 27C with a humidex of 28 means that humidity is not really an issue since the humidex is not adding much to the actual temperature. So if humidex is not a factor, why mention it? (Same goes with mentioning windchill in the winter when winds are light.. not a factor, so why mention it?) In my opinion, humidex should only be mentioned if it's >=3C from the forecast temperature, AND if it's >= 30C (humidex table shows "no discomfort" if humidex value < 30C)
ReplyDeleteHere's the general breakdown regarding humidex and the difference between it and the actual air temperature..
DeleteIf humidex is within 4C of the actual temperature, then the humidity is quite comfortable relative to the air temperature, and humidex is NOT a factor. In fact, humidex shouldn't even be advertised in these cases since it gives the misleading impression that it's actually humid when it isn't.
Humidex 5C higher than temp: somewhat humid, still comfortable for most
6C diff: moderately humid, becoming uncomfortable
7C diff: humid, uncomfortable
8C diff: quite humid, quite uncomfortable
9C diff: very humid, very uncomfortable
10+C diff: extremely humid, oppressive
These are based on the DEWPOINT which is a much better measure of how "muggy" an airmass feels. Dewpoints < 15C are quite comfortable, even if it's 35C (a "dry" heat). On the other hand dewpoints > 20C are uncomfortable since the increased moisture in the air makes it more difficult for perspiration to evaporate from your body (which is what makes you feel cooler) This makes conditions feel quite muggy even if air temps < 30C. Once the dewpoint > 22-23C, you're into "oppressive" conditions where you'll just be constantly perspiring with any physical activity, which can lead to heatstroke if prolonged.
Latest 4km NAM guidance for Thursday suggests strong to severe tstorms erupting around the Yorkton-Roblin area late afternoon then moving southeastward across the Riding Mountain Park area early Thu evening before convective complex pushes into the RRV by midnight as a line of storms with frequent lightning, heavy downpours, and possible damaging wind gusts and large hail. That's the general idea anyways.. we'll see how things actually develop tomorrow evening.
ReplyDeleteLatest guidance has shifted the highest threat of severe thunderstorms over SW MB this evening (Virden, Melita, Pilot Mound, etc) with strongest storms tracking east tonight across southern RRV. Winnipeg still has a chance of storms but higher threat likely to our south and west.
DeleteI'd say yesterday's event was rather a bust in Southern Manitoba. Way too much hype this week once again for what was virtually a non-event except for those few severe cells in Southwest MB during the evening.
ReplyDeleteWell it wouldn't be the summer convective season without storms skimming all around the city like they did last night lol.
ReplyDeleteHigh pressure quickly build down overnight ushering a considerably cooler airmass for tomorrow. Next disturbance starts moving in from Wyoming, and tries to push the warmer, muggy air back north overnite Saturday. Strong 60-65 kt LLJ cranks up with models showing a large areas of elevated convection moving eastwards. Best forcing looks to stay west and then possibly weaken by the time the convection reaches RRV or SE Manitoba. More elevated convection may fire up again Sunday evening over SE Manitoba and NW Ontario.
Any surface based convection should stay south of the border with the warm sector only brushing our region. Other area of interest would be inverted trough connecting the Northern Plains low with another in Alberta, but heating and instability look limited along this trough line
Large area of precipitation coalescing in SE Saskatchewan, with LLJ wrapping around disturbance and plenty of mid-level forcing. That area should move up into western Manitoba and miss our region. Models suggest eastward development of elevated convection along 850 hPa warm front after 3-4 AM for our region.
DeleteThere will be a lull around midday before elevated convection starts redeveloping between 1-4 PM in the RRV. Uncertainty as to where and when exactly, but potential for heavy rain is there in the afternoon/early evening hours.
Also of interest will be how far north any clearing and surface based instability can get. Models show it staying south of Fargo, but with surface low hanging up and tracking into the SE corner of the province.. trends will have to watched for any clearing in NW Minnesota and advection of severe cells into far SE Manitoba.
Split SW flow continues, with large upper low over BC and upper trough over Desert Southwest. Energy consolidates around disturbance moving up in southern stream.. resulting in a closed circulation and vertically stacked low which will track towards the Northern Plains before slumping to the southeast again. As a consequence, model QPF fields show no to trace accumulations for the Winnipeg area, with a large QPF maximum across the border (brushing southern RRV and SE Manitoba), and under the northern stream upper low in Alberta.
ReplyDeleteHowever, given the complexity of the flow (with the southern disturbance projected to turn back south at some point), and the lack of a sharp moisture/dewpoint gradient north of the border.. wouldn't be terribly surprised if showers and precipitation creep a bit further north. Something to watch tomorrow as area of showers moves north Tuesday evening.
hmm.. interesting
DeleteWell advertized severe weather threat overnite.. approaching area of convection now crossing into Manitoba from Saskatchewan.
ReplyDeleteHighest resolution (<= 4km) models disagree considerably w.r.t. key parameters such as 12 C 700 hPa isotherm and position of LLJ. Southern edge of storms just north of the former feature (cap) and on the nose of LLJ. HRRR has better handle on current convection, with 4 km NAM not progressive enough on storm motion.
4km NAM is further north with mid-level cap and has a stronger and further north LLJ.. HRRR further south. If the latter solution is correct (given that this model is initializing better), bowing complex will drop south towards N Dakota into its moisture source as cells propagate down into LLJ - with a general heavy rain/ hail threat for Winnipeg. More northern scenario would have strong wind threat for southern RRV and as far north as Winnipeg.
Radar trends in the next hour or so will be key as to any southward motion on storms and position of cap and LLJ.
Another round of active weather and potential for heavy rain for this weekend.
ReplyDeleteMain threat appears to be elevated convection overnite Friday into Saturday. Moisture and instability start building tomorrow as we tap a southerly flow, but with surface warm front well to our SW; and remnant weak convection associated with LLJ; there will likely be cloud cover to deal with, and limited surface based triggers.
LLJ retrogrades and intensifies late Friday as disturbance approaches from N Dakota. Severe elevated convection (hail, heavy rain) will be possible Friday evening thru the overnite - until the LLJ finally transits east by dawn Saturday.
Will get muggy by midday Saturday as we briefly tap the warm sector. Cold front should be through by early afternoon.. so risk for any severe surface based convection will be over SE Manitoba and NW Ontario. Wrap around moisture and showers for overnite Saturday into Sunday.
A few lines of elevated convection passing through on the nose of the LLJ, and along the 10 C isotherm at 700 hPa. Main show still potentially later overnite.
DeleteLLJ ramps up to 45 kts and remains stationary until around 6 AM. This feature has the potential to interact with an area of surface based convection over Saskatchewan, that will move east and likely evolve into an elevated MCS. Complex progged by some high resolution models to propagate east across S Manitoba north of the mid-level cap.. bringing threat of heavy rain. Most likely timeframe would be between 3-5 AM locally, but scattered cells cannot be ruled out anytime between now and dawn.
Anonymous.. appreciate your posts. I have little time in the summer to update this blog during active convective periods, so any input is appreciated.
DeleteThings worked out pretty much as you said.. with a derecho type severe wind event over much of southwest MB into the southern RRV (wind gusts of 90 to 125 km/h), while a band of elevated convection Friday night produced tremendous rainfall over the Whiteshell area (140 mm in the West Hawk Lake/Falcon Lake areas), including a whopping 100 mm between midnight and 2 am.
On a longer term basis this article and map imlies that the odds against a large number of 30 degree days this summer have been diminished
ReplyDeletehttps://www.climate.gov/news-features/blogs/beyond-data/day-and-night-how-summer-afternoons-listen-spring-rains-and-nights
Rob does your experience match this. With lower summer maximums following heavy spring rains
ReplyDeleteWhile waiting for your answer i looked at the last time we went through heavy spring AMJ rains in 2010 and found 9 or 10 >30C days in July and August, pretty average I would guess. We ended up with close to 750 mms of rain that year of dimishing El Nino and a Modest La nina.
ReplyDeleteDon.. I'll have to dig a little deeper into the stats to come up with a more definite answer, but certainly soil moisture is a key component for driving summertime convection (both in terms of evaporation, and also increased transpiration from crops) The wetter the soil at the beginning of the growing season, the more likely you'll have increased convection and summertime precip. That would tend to lower summertime temperatures with increased convection/precip.. but not always. Conversely, when you have dry soil conditions, the harder it is to drive convection, and the more likely dry condition will continue (drought begets drought). This can lead to increased summertime temperatures since there's less cloud and precip to block solar heating (and dry conditions allow for greater heating at the surface compared to moist conditions).
DeleteDon..
DeleteI crunched some numbers and the results may surprise you. Basically, total spring precip (AMJ) had no noticeable effect on ensuing summer heat. On average, Winnipeg gets about 9 days of 30C or more in July and August. Of the 10 driest AMJ periods, 4 years had above normal "hot days" in July/Aug, while 4 had below normal amount, and 2 were average. Of the 10 wettest AMJ periods, 5 years had above normal hot days in Jul/Aug, while 3 were below normal and 2 were average.
Avg # of hot days in J/A after dry spring: 11
Avg # of hot days in J/A after wet spring: 10
30 year average: 9
So basically, total spring precip is not really a good indicator of how hot the summer will be. That's likely because spring precip, especially in May and June, can be so convectively driven which can inflate precip totals but not necessarily indicate a cool trend for the summer.
On the other hand, the 2 hottest summers (in terms of 30C days) followed dry springs (2006 and 1961) so the argument can be made that the chances of a hot summer are increased with preceding dry conditions.
Thanks for that explanation Rob .I see we managed to join the 200mm club but took 34 days to do it. We are well on our way to repeating the summer and fall of 2010. As always though this one will be different. Enjoy your posts and tweets very much .
ReplyDeleteThanks Rob..I would add 1936 to those hot dry springs as well though i am sure it was outside the search parameters and records were St Johns .
ReplyDeleteAnother Question if i may, about that Derecho on friday night and Saturday. How far did it travel and did it include the Whiteshell Falcon Lake deluge and Flash Flooding at Caddy Lake .
Don.. yes, I only analyzed Winnipeg airport stats from 1938 to 2015. 1936 was certainly another scorching summer after a dry spring.
DeleteThe derecho event on Friday night tracked from Montana across western ND and SW MB early Saturday morning and into the southern RRV. The complex of thunderstorms continued into SE MB early Saturday but we don't have many reports of wind damage over SE MB with it. The major flooding event over Falcon and West Hawk lakes was due to a separate band of thunderstorms that intensified northeast of Winnipeg late Friday night and tracked east into the Whiteshell. This was associated with a band of elevated convection that basically sat over the West Hawk lake area of 2 hours early Saturday morning, dumping over 100 mm of rain between 1230 and 230 am. It was separate from the derecho that produced all the wind damage over SW MB.
Line of surface based convection getting going off to our west, with strongest storms right now in N Dakota. However line of convection extending to the NE should begin to rapidly intensify with SBCAPE of 4000 j/kg and 3500 MLCAPE over RRV, as per mesoanlaysis and backed up largely by soundings from Winnipeg. There is also minimal to no cap with 700 hPa temperatures only at 7 C..
ReplyDeleteStorms are starting to split around the city (again).. with a line forming just north and northeast of the city, and also SE.
ReplyDeleteTrough still appears to be in western RRV and there is one cell just SW of the city to keep an eye on..
Next system poised to move through tomorrow, with upper flow turning SW ahead of the disturbance. Elevated convection tonite should stay to our south with LLJ and instability down over the Midwest.
ReplyDeleteTomorrow the surface low becomes better defined, and the entire system starts becoming vertically stacked. Will have to watch for any convection that blows up over the Dakotas and Minnesota to coalesce into area of stratiform rain with embedded convection. This area of precipitation is progged to back into SE Manitoba - possibly as far as RRV and Winnipeg - by afternoon as the system winds up. This morning's and afternoon's model runs were showing between 10-30 mm depending on exact placement of that band
Area of showers and rain over the southern RRV and border counties of N Dakota. Precipitation shield should pivot around as system wraps up this evening. Deformation rain band will set up and linger over SE Manitoba. Highest resolution models keep most of the precipitation southeast of Winnipeg, but will have to keep an eye on it..
DeleteMassive bow-echo/derecho ongoing over N Dakota. 300-850 hPa flow would advect it into S Manitoba, but this is unlikely to occur due to a couple of factors. The nose of the LLJ will likely not penetrate north of the international border, allowing cells to propagate down into the US and cause the entire complex to move east rather than NE. This motion is being reinforced by cold pool development and orientation - which is also breaking the cap further south (where 700 hPa temps are in the mid-teens).
ReplyDeleteFor Winnipeg, more scattered convection producing heavy rain will be possible, but forcing or organization will likely not be as impressive as what is occurring states side right now..
Can someone please explain to me why all the good storm activity seems to always stay states side? Not just last night but like in every severe weather scenario set up where southern MB is included? This has been the case for such a long time now.
DeleteAnonymous.. That's not always the case, but it often happens when the main jet stream/storm track sets up along the international border which keeps the greatest energy/instability for the most severe storms state side. Occasionally this storm track will lift north, and the strongest storms will develop over southern MB.. but generally, the greater odds for severe storms will be closer to the US border (southern RRV, SW MB)
DeleteBut why does the storm track or main jet stream favor that area in particular over a long period of time? Is it just a weird cycle we've been stuck in for a number of years or has it just always been that way with no real explanation as to what causes it to always track through those areas?
DeleteMainly it's due to climatology.. the main area of severe thunderstorms shifts from the southern plain states in the early spring to North Dakota by mid July before it starts retreating back south again in August. It's possible this storm track may exhibit extended periods or cycles that favours one area over another, but generally, it's just a of byproduct of the climatology of this region.
DeleteOk. So the main area of severe thunderstorms don't quite reach across the border? Manitoba's climatology changes that much from North Dakota?
ReplyDeleteI should have said the North Dakota/southern MB area.. it's not a set boundary at the international border. Climatologically though, the odds of severe storms increases as you go south.
DeleteIt makes sense I guess. Thanks for taking my questions. Lol I'm just starting to feel a little storm deprived and are trying to understand the whole thing. You don't have to go that far south it seems to be in the prime area all the time. For someone who loves storms, its frustrating that we are ever so slightly on the wrong side of the "storm border", being so close yet so far to having awesome storms all the time (as been the case in North Dakota) or having very little. And we don't usually get good storms without them getting it first it as well it seems. Like seriously they seem to get as many storms now as Oklahoma gets in the spring. Just wish that kind of (consistent) activity extended just a bit further north, climatology speaking. I guess that's not going to change anytime soon though.
ReplyDeleteLarge area of elevated convection on nose of LLJ over central Minnesota, while upper low spins over Saskatchewan. We're in a no man's land of sorts right now.
ReplyDeleteMain issue would be any potential development along the surface trough off to our SW. Some convection over western Dakotas, but even this looks elevated on radar. With the LLJ veering well east into the Great Lakes overnite.. feel that high resolution models like HRRR are overdoing potential for that convection to affect our region tonite. Copious boundary layer cloud has prevented surface based destabilization, and without much forcing - will likely only see scattered/isolated elevated cells moving through.
That line of convection holding together fairly well.. likely being supported by left exit region of 500 hPa upper jet. Still wouldn't rule out some weakening to more of a broken line as it approaches our area - with instability starting to run out.
DeleteWind gusts up to 60 km/h reported in N Dakota, but storms have not attained severe parameters, and there are no warnings out by NWS. Should be over Winnipeg within the next 1 to 1 1/2 hours..
..and no sooner had I posted that, the NWS issued a severe tstorm warning for a cell crossing into Manitoba at 9:15 PM lol. 90 km/h wind gusts and severe hail noted.. we'll see if it holds together.
DeleteReally getting tired of this constant convection.. boy I would love a 4 week spell of straight sunshine and heat.
ReplyDeleteYeah, I agree with you Rob. It really hasn't been much of a summer thus far. We had that warm May but really since then, it's not been that great. We are really struggling to get Temps above 25C this summer. Not sure how the rest of the summer will play out bur there does not appear to be any sustained heat in the works for us anytime soon. There may be a glimmer of hope for a stretch of sunny and drier weather next week but I wouldn't count on that happening just yet. And even if that does happen, it will be short-lived as it looks like the last week of July turns stormy again.
ReplyDeleteSummer is on hold for the next few days as a large upper low tracks across Manitoba bringing cool unsettled weather over us. Tomorrow (Wednesday) will feel more like a fall day than summer with overcast skies, occasional showers, brisk northwest winds, and temps in the teens. Yuck. Ridiculous that the forecast for tomorrow mentions humidex.. that's the last thing people will be worried about tomorrow (that or UV). Things will slowly clear out Thursday afternoon (hopefully) before we finally get a stretch of sunny weather Friday into the weekend that hopefully extends into next week. Since Victoria Day, Winnipeg has seen only 1 stretch of 4 rainfree days in a row (June 13-16) otherwise, we've had measurable rain every day or two. Enough already.. I realize June is our "monsoon" season, but it sure would be nice if Mother Nature moved the sprinkler to southern Ontario where they need it!
ReplyDelete