Monday, March 16, 2009

Flood risk increases over southern MB



The province of Manitoba released its updated flood outlook today, and it is indicating that this years spring flooding in the Red River valley will likely approach 1979 and 1950 levels, the worst floods on the Red apart from the record 1997 flood (and the historic 1826 flood before Winnipeg was a major settlement). Flood forecasters say even with favourable weather conditions in the next few weeks, major flooding is likely this spring. Another major snow or rain storm may push flood levels toward 1997 levels especially towards the US border. Long range weather models are hinting at the development of a significant storm system moving across the plains/Prairies early next week with the potential for significant amounts of rain and/or snow across the Red River valley. This situation will be monitored closely as it will have a serious impact on the flooding situation should heavy precipitation develop. Stay tuned.

31 comments:

  1. Looks like we will get another day of melting even up here tomorrow. Core of cold advection stays north with 850 hPa temps around -4 C. With westerly flow and degraded snowpack I think temps will sneak up to 2 C. Snowline has retreated a good 200 - 300 km north this weekend. Bare ground now almost to N Dakota/ S Dakota border...

    ReplyDelete
  2. Nice area of precip moving through the Southern Forecast Area...WE DON'T NEED ANY RAIN!!!

    Here's an excerpt from the NWS Forecast Discussion in Grand Forks...


    414 PM CDT MON MAR 16 2009

    ...WARM WEATHER BEGINS SOME MELT AND WATER MOVEMENT...
    ...SIGNIFICANT STORM POSSIBLE LATE IN THE WEEKEND INTO NEXT WEEK...

    THE RECENT WARM WEATHER HAS STARTED THE SPRING SNOW MELT PROCESS.
    AS MOST RURAL DRAINAGE CHANNELS...RIVERS AND STREAMS REMAIN CLOGGED
    WITH ICE...LOOK FOR ADDITIONAL OVERLAND MOVEMENT OF WATER...WITH
    INCREASED PONDING IN LOW SPOTS. WARM WEATHER WILL LIKELY NOT BE
    SUFFICIENT TO START THE REAL SNOW MELT FLOOD FOR THE MAIN RIVER
    SYSTEM UNTIL LATER THIS WEEK AND INTO THE WEEKEND.

    THE REMAINDER OF THIS WEEK SHOULD SEE QUIET WEATHER WITH NO
    SIGNIFICANT PRECIPITATION EXPECTED. FLOOD FIGHTERS SHOULD MAKE
    MAXIMUM USE OF THIS PERIOD TO ACCELERATE DIKE PREPARATIONS.

    A POWERFUL STORM SYSTEM CURRENTLY WELL OFF THE WEST COAST OF THE
    UNITED STATES IS FORECAST TO MOVE INLAND LATE THIS WEEK. IT WILL THEN
    SPREAD INTO THE PLAINS STATES BY EARLY NEXT WEEK. AHEAD OF THIS
    STORM...STRONG SOUTH WINDS SHOULD DEVELOP...BRINGING WARM AND MOIST AIR
    INTO THE REGION. THIS MAY SET THE STAGE FOR SHOWERS AND POSSIBLY
    THUNDERSTORMS LATE THIS WEEKEND INTO EARLY NEXT WEEK. AS THE LOW
    PRESSURE CENTER MOVES THROUGH...SIGNIFICANT PRECIPITATION AMOUNTS
    IN THE FORM OF RAIN OR RAIN MIXED WITH SNOW MAY OCCUR.

    IF THIS STORM DEVELOPS AS CURRENTLY FORECAST...IT COULD HAVE A
    SIGNIFICANT IMPACT ON AREA FLOODING. RESIDENTS OF THE RED RIVER
    VALLEY REGION ARE ADVISED TO PAY CLOSE ATTENTION TO LATER
    FORECASTS. YOUR NOAA`S NATIONAL WEATHER SERVICE WILL CONTINUE TO
    MONITOR THIS SITUATION AND PROVIDE UPDATED STATEMENTS AND
    FORECASTS ON THIS DEVELOPING SYSTEM.

    ReplyDelete
  3. Another excerpt...

    LONG TERM...THE MAJOR CONCERN IN THE LONG TERM IS THE DEVELOPMENT
    OF A MAJOR CYCLONE EVENT FOR THE NORTHERN PLAINS SUNDAY INTO
    MONDAY. THIS SYSTEM HAS REMAINED CONSISTENT FOR SEVERAL DAYS IN
    THE FORECAST MODELS. THIS STORM WILL BE ABLE TO TAP GULF OF MEXICO
    MOISTURE AND DRAW UP PRECIPITABLE WATER VALUES IN EXCESS OF ONE
    INCH. IN ADDITION...850 MB SHOWALTER VALUES SUGGEST THE
    POSSIBILITY OF ELEVATED THUNDERSTORMS WITH THIS SYSTEM SUNDAY NIGHT.
    PRECIPITATION AMOUNTS ARE EXPECTED TO APPROACH A TWO DAY TOTAL OF
    AT LEAST 1.25 INCHES AT THE PRESENT TIME. THIS WILL AGGRAVATE THE
    SNOW MELT FLOOD SITUATION ACROSS THE ENTIRE RED RIVER BASIN.

    ReplyDelete
  4. Ensemble plot shows a large area of at least 10 mm of precipitation over southern MB for the 23rd, which is quite significant for an ensemble forecast this far out. For Winnipeg, ensembles give a 50% chance of at least 10 mm of precipitation, with a 25% chance of 30 mm or more. GFS is showing a major storm moving through southern MB with heavy rain followed by heavy snow..while the GLB has more of a rain event with an inverted trof, before system weakens as it moves into Manitoba. Suffice to say, heavy pcpn potential is there.. details will become clearer in the days ahead.

    ReplyDelete
  5. Arctic front came thru this morning with above freezing temps until 7 AM. Temperatures clawing their way back up. Still think at least 0 C is possible especially in the city.

    Once again the snow depth estimate at YWG appears wonky (satellite estimate?). Depth only dropped from 17 to 14 cm. Rob and others.. what are your current snow depths? Hard to estimate where I'm at.

    ReplyDelete
  6. Yeah.... the GFS is showing quite the storm with a heavy wind swept rain turning into a wind driven snowstorm!!!
    Either way it could be bad news!

    ReplyDelete
  7. Daniel..

    Snowdepth at my place is quite variable owing to drifting and varying exposure.. but I'm around 20 cm snowdepth on average.. which is down about 8 cm since Friday.

    ReplyDelete
  8. Speaking of snowcover.. it's remarkable how quickly the snow has disappeared in the Red River valley basin of North Dakota. Satellite pix show quite a bit of bare ground from near Fargo to Emerson.

    ReplyDelete
  9. The GFS has been quite wacky with this system so far, with little run-to-run consistency. 06Z today showed about 50mm of accumulation around the RRV, now it shows <12mm (12Z run). I am very curious to see what the 18Z run brings.

    The GEM on the other hand, has been fairly consistent. Last night's 00Z run showed 50 to 75mm of rain over the Manitoba RRV, with <40mm generally over ND and MN. I have a hard time believing that 50 to 75mm could fall this early in the year...that is even a long shot for a June storm. There is no doubt that a large storm will impact the northern plains early next week, the question is now about who will get the worst of it.

    P.S. The GFS is also showing highs of about +9, +11, and +11 for Friday, Saturday, Sunday for SE MB (subtract appropriately for YWG). It also shows 500 J/kg of MLCAPE for SE MB with the storm. Severe thunderstorms anyone?

    ReplyDelete
  10. This system will be a double whammy.. 2-3 days of mild temperatures along with dewpoints well above zero will lead to a rapid snowmelt, with a good liklihood of significant rain in a swollen river basin. Not looking like a good scenario. That investment in an expanded floodway may be paying off much sooner than anyone expected.

    ReplyDelete
  11. You got that right Rob!

    This whole situation is looking a whole lot like 1997. It is March and we are already bracing for a big flood, then a large storm hits and we are in an emergency. However like I have said before (and what Provincial officials have said), even a 1997 level flood shouldn't even concern Winnipeggers, since the floodway has more than twice the capacity it had in 1997. Most rural communites have dikes that are several feet higher than 97' levels, and most homes around the Red River are safe. I think I heard that 85% of Red River Valley residents are safe from flooding now, and the remaining 15% will get plenty of help.

    ReplyDelete
  12. Latest guidance hinting that this will be a double barreled event.. with rain developing Monday-Tuesday ahead of an inverted trof, changing to snow by Wednesday as main low moves into Minnesota. Models hinting that the heaviest rain may be displaced north and west of the Red River valley through Interlake/central MB areas which would be a good thing.. but the wild card is what may happen with convection in the warm southerly flow ahead of this system. That may bring heavier rain through the Red River valley over what models suggest. Main low over central plains then moves into Minnesota Tuesday into Wednesday bringing colder air and snow into southern MB.. with significant amounts possible. Still lots of uncertainty with regards to precip amounts for the RRV.. but a sustained melt looks like a sure bet over the weekend through Tuesday, with precip amounts of 15-25 mm likely between Monday and Wednesday.

    ReplyDelete
  13. Here are some snowdepths around the Red River valley as of this morning..

    Portage LP .... 21 cm
    St Alphonse ... 15 cm
    Carman......... 10 cm
    Miami.......... 9 cm
    Winkler........ 3 cm
    Snowflake...... 18 cm
    Oakbank........ 18 cm
    Wpg Arpt....... 14 cm
    Wpg Chwd....... 20 cm
    Piney.......... 12 cm
    Grand Forks.... TR
    Fargo.......... 10 cm

    Satellite photos indicate lots of bare fields appearing towards Emerson-Gretna area. Look for these areas to be several degrees warmer than nearby snow-covered areas especially on sunny days with light winds.

    ReplyDelete
  14. how could grand forks only have a trace of snow (TR) when they just had a big blizzard a couple of weeks ago?????

    ReplyDelete
  15. Thanks for the snowdepths Rob. I am surprised that relatively little melting has occurred in the Winnipeg area. Temperatures and wind conditions were similar at Winnipeg, Grand Forks, and Emerson at least until Tuesday morning. So why did much more melting occur at Emerson and Grand Forks by that time?

    ReplyDelete
  16. In my backyard there is about 20cm, but in other spots there is bare ground, so I don't really know what my snow depth would be. On average I would say that 10-15cm is a good guess.

    I don't expect to have any snow by next Monday.

    ReplyDelete
  17. Grand Forks didn't have much on the ground before last week's blizzard.. and even then, they only got about 5" (13 cm) from the storm. More fell to their south and east. The weekend thaw and sunshine got rid of most of that snow in GFK fairly quickly.. as it did over the south end of the RRV in MB. I must admit though I was surprised to see it go so quickly..

    ReplyDelete
  18. Precip predictions for Grandforks for 7 of the 8 days beginning Friday

    ReplyDelete
  19. Interesting... soon we'll starting melting again as suggested already.
    That upcoming storm system is looking very complex. GFS is having difficulty resolving exact pressure and precip pattern. As Rob mentioned there will be two main pieces of energy.

    The lead disturbance will eject thru Alberta and Saskatchewan on Sunday. In response to this upper forcing an inverted trough (previously depicted as a discrete Montana low) will set up at the surface over Saskatchewan. This will pump warm air over the eastern Prairies helping us melt more snow. Mid level forcing (frontogenesis) will generate a large area of defromation zone snow (cold 850 hPa temps)over Saskatchewan and eventually Central Manitoba.

    Then the big player enters the stage... main upper wave generates Colorado type low which moves into central plains. Very impressive low level jet forms out ahead of it. Warm air and deep moisture (850 hPa dewpoints approaching 10 C!) surge north into SE Manitoba overnite Monday into Tuesday morning. Isentropic lifting of the unstable moist air, and mesoscale forcing (convergence form nose of LLJ) all target SE Manitoba. The result could well be severe elevated convection RRV/SE Manitoba.

    Deformation snow band sets up over interlake and SW Manitoba in response to mid level frontogenesis etc. Looks like Winnipeg will be sitting with light drizzle and slightly above 0 C temps as main forcing stays off to NW...

    In summary for Winnipeg/RRV... severe elevated storm potential overnite Monday with heavy rain and hail as main threats... followed by dry slot/light precip with significant snow band off to the northwest. Now watch that completely change as the next runs come in.

    ReplyDelete
  20. About snow depth at Grand Forks....always a topic for discussion as always depend on where you measure. Our measuring area for snow for NWS is an open field to the east of the office away from trees...and as such is often wind blown and thus does not accumulate much in wind storms or it gets blown away. In open areas where snow depths were low due to exposure from the wind...there is no snow attm...but in town and sheltered areas where less affect due to wind there is still several inches of snow there....with of course drifts still around. So our Trace of snow depth is accurate for our measuring area...but if you would measure in town or in your backyard where trees are present it would be closer to 3-4 inches. As with the last blizzard and the wind...at my house you either had one inch on the ground or you had 3 feet...take your pick.

    ReplyDelete
  21. On a related note....fields are pretty bare now...as the snow blew off of these areas on the last event.

    On a side note...in regards to flooding numbers out there....there is some discussion on what if the river models used at the RFC in Chanhassen MN are incorrect in assuming the Nov pcpn is frozen still in the ground. Without the storm coming up....most of these high numbers are predicated on the fact there is high soil moisture with the fall rain iced up in the soil and ready to flow again.. Could we have egg on our face if the high numbers do not occur??

    ReplyDelete
  22. Lets see "egg on face" if too high a prediction or CATASTROPHE if too low??

    ReplyDelete
  23. Difficult to overstate the flood threat when NWS FGF Long Term at 4am is saying 50 to 70mm rain Sunday thru Tuesday in the Valley.

    ReplyDelete
  24. The situation is looking more and more dire by each passing model run!

    The flooding potential has gotten a whole lot worse with this upcoming storm!

    ReplyDelete
  25. The folks at the River Forecast Center in Chanhassen ran some river models with 1-1 1/2 inches of rain and it did push the Red in Fargo to around 40 ft a week from this upcoming Saturday... This was told to the Mayor late Wed aftn and this morning from 9-10 am there was a city meeting and after that the call went out that for a 40 ft crest there would need to be 1.5 million sandbags. The official info on the web as yet to be sent out...the NWS in Grand Forks gets info from the RFC and they send it to us and we sent out the statements. Our job is to coordinate with all agencies to get the word out and to focus on rainfall from the next system. I worked last night and the ecmwf and 00z gfs had a 2-3 day total of 2.25 to 2.75 inches. Now if that is true it would indeed be big trouble for Fargo as there is lots of water upstream in the snow in the Sheyenne that has not melted yet. So Fargo may get a 1-2 punch. We hope that it doesnt come to that though...

    ReplyDelete
  26. Interesting how a blowing snow event can effect melting patterns by lowering snow depth over large areas.

    Details still not very clear on the upcoming system but general idea is similar. Arctic front sneaks thru late Friday leading to a cool Saturday with a dry NE flow. Real warm-up occurs on Sunday/Monday as we tap a moist southerly flow ahead of an inverted trough over Saskatchewan.

    Trough appears to drift slowly eastwards with stratiform type precip on the cold side. At the same time the main Colorado low ejects out of the central plains.

    The best moisture/instability would stay east of the low track along the surface and 850 hPa warm fronts. Models suggest a track thru Minnesota which may put Manitoba into more of a steady precip event. Of course specifics cannot be pinned down yet.

    ReplyDelete
  27. Latest GFS is decidedly colder with a more SE track for the low... NWS at Grand Forks also discussing this. In fact Winnipeg is now barely in the heavy snow band. Will have to see if trend holds ..if so, we are looking at a heavy snow event over the RRV/ SE Manitoba. Convective threat would be confined to WC Minnesota. Lets see...

    ReplyDelete
  28. The 12Z run showed about 30cm of snow with this system for southern Manitoba. Guess what...The 18Z run shows absolutely ZERO accumulation. I don't know how the models can shift so much over 6hrs, it is beyond me.

    ReplyDelete
  29. Rob, it's time to start a new entry...this comment section is getting to long. Give some insight as to what you might think. Maybe address the likely tornado outbreak for monday-tuesday...it's nice to hear from a meteorologists perspective

    ReplyDelete
  30. Will do.. new thread to start..

    ReplyDelete
  31. Hi!

    Mansour Engineering have a refined understanding of client and market priorities in all facets of mechanical, electrical and civil engineering from engineering assessments and studies through typical and specialized design commissions, document production, contract administration, design/build, energy studies, field inspection and supervision, to building systems commissioning and consulting services for building operations.

    [url=http://www.mansour.ca] click here to go to Mansour Engineering[/url]


    http://www.mansour.ca

    ReplyDelete