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January 20-? Cold snap


Ottawa Blizzard

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Steady at -3° here today.

 

WC have been shy of the warning criteria today so far.

 

Cold update from LOT. Sounds like warmer over night lows now.

 

 

.DISCUSSION...
1148 AM CST

THE FORECAST HAS BEEN UPDATED THROUGH EARLY EVENING TO REFLECT
WARMER TEMPERATURES BY ABOUT 3-7 DEGREES. THIS RESULTED IN MILDER
WIND CHILL VALUES. CERTAINLY STILL BITTER COLD...BUT WIND CHILLS
VALUES THE REST OF TODAY LOOK TO BE MORE IN THE -15 TO -30...FROM
SOUTH TO NORTH...ACROSS THE FORECAST AREA.

IMPRESSIVE DEEP UPPER AND COLD TROUGH COVERING THE EASTERN THREE-
QUARTERS OF NORTH AMERICA THIS MORNING. THE CENTER OF THE CURRENT
POLAR VORTEX LOBE LOOKED TO BE MEASURED AT CWPL IN WESTERN QUEBEC
WITH -48C AT 500MB. IN A LITTLE OVER TEN YEARS OF FORECASTING
HAVE NOT SEEN THAT COLD OF AIR AT 500MB THAT CLOSE TO THE CONUS.
IN THE LOWER LEVELS...1037MB ARCTIC HIGH IS ANCHORED ACROSS THE
PLAINS STATES WITH CONTINUED NORTHWEST WINDS OVER THE CWA...MAINLY
AT 15 TO 20 MPH AND GUSTS TO 25 MPH AND SPORADICALLY 30 MPH. WHILE
THERE REMAINS COLD AIR UPSTREAM AT THE SURFACE...THE ACTUAL
PRESSURE RISES HAVE SLOWED ACROSS THE REGION. IT APPEARS THE
NEARLY FULL SUNSHINE IS ENOUGH TO OFFSET...JUST BY A SLIGHT
AMOUNT...THAT SURFACE COLD AIR ADVECTION. IN ADDITION...AT
850-950MB THE THERMAL ADVECTION LOOKS TO BE NEUTRAL...SO THAT IS
NOT HELPING TEMPERATURES TO CONTINUE TO FALL.

IT APPEARS SOME OF THE MODELS ARE ANALYZING MORE SNOW COVER THAN
ACTUALLY EXISTS AND WE BELIEVE THAT COULD BE INFLUENCING THEIR
SURFACE TEMPERATURES TO BE TOO COLD...INCLUDING MOST RAW GUIDANCE
WANTING TO SHOW A DROP THIS AFTERNOON. THIS PROBLEM WITH TOO COLD
OF A FORECAST BY RAW MODEL OUTPUT VERY WELL COULD CONTINUE TONIGHT
INTO TUESDAY. WILL CONTINUE TO MAKE SOME FORECAST ADJUSTMENTS
INTO EARLY THIS AFTERNOON BASED ON OBSERVATIONAL TRENDS AND
CLIMATOLOGY WITH THESE 925MB/850MB TEMPS OBSERVED THIS MORNING.
THE LOWEST WIND CHILLS STILL LOOK TO BE OVERNIGHT THROUGH ABOUT 9
AM TUE...WITH -25 TO -40 FROM SOUTH TO NORTH...WITH MUCH OF THE
CHICAGO AREA -30 TO -35...AND POSSIBLY -40 IN THE NORTH.

MTF

 

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Similar to the cold blast in early January, we did not get as cold as expected this morning and we warmed more than expected during the day.  A day or two ago DVN had a high today of about -8, but it has risen to -1.  Maybe we are too close to the edge of the snowpack.  Even the snow we do have is pretty thin.

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LOT sticks with -15 to -20 tonight, with temps at and above 0 tomorrow...

 

THE ABSOLUTELY MASSIVE UPPER TROUGH THAT IS COVERING THE EASTERN
80 PERCENT OF NORTH AMERICA OR SO IS NOW EVER SO SLOWLY INCHING
EAST. ONE POCKET OF THE COLDEST 850MB TEMPS AT -28C TO -32C AND
925 MB TEMPS AT -25C TO -30C ARE ROTATING EAST OVER THE GREAT
LAKES REGION WITH MORE OF NEUTRAL TEMPERATURE ADVECTION AT THAT
LEVEL GOING INTO TONIGHT. THE 1034MB SURFACE HIGH ACROSS THE
MISSOURI RIVER VALLEY WILL EXPAND EASTWARD ACROSS CENTRAL IL BY
DAYBREAK TUE. SO WE SHOULD SEE WINDS GRADUALLY DIMINISH IN
INTENSITY TONIGHT...AND EVEN DROP DOWN TO AROUND 5 MPH ACROSS THE
SOUTHERN HALF OF THE CWA LATE. TEMPERATURES SHOULD FALL OFF
NICELY AFTER SUNSET...WITH THE COMBO OF NIGHTFALL AND SURFACE COLD
AIR ADVECTION THIS EVE...AND THEN THE LACK OF PRESSURE GRADIENT
FURTHER INCREASING THE COOLING OVERNIGHT ESPECIALLY SOUTH. MODEL
GUIDANCE IS LOCKING ON A BIT BETTER THAN EARLIER WITH SURFACE
TEMPS BUT STILL SOME LARGE SPREADS. CLIMATOLOGY FOR THE 925MB AND
850MB TEMPS FORECAST TONIGHT...WHICH ARE AT THE TAIL END FOR THIS
COLDEST TIME OF THE YEAR...MINS LOOK TO STILL FALL OUT -15F TO
-20F ACROSS THE AREA WITH A FEW LOCATIONS DROPPING JUST BELOW.
THIS SHOULD RESULT IN SOME LOCATIONS BREAKING RECORD
TEMPERATURES...INCLUDING CHICAGO. IMPRESSIVE TO DO AT THE NORMAL
COLDEST TIME OF THE YEAR. MINIMUM WIND CHILLS FALL OUT TO -30
SOUTH TO -40 NORTH LATE TONIGHT INTO TUE MORNING.

WHILE THE PATTERN WILL FAVOR GRADUAL MODERATION OF THE ATMOSPHERE
ON TUESDAY...THE VERY LOW STARTING POINT MENTIONED ABOVE WILL
LIMIT HOW HIGH TEMPS WILL GET. THE DIURNAL RANGE THIS TIME OF YEAR
IS MINIMAL IN THE ABSENCE OF WARM AIR ADVECTION. SO CONTINUE
FORECAST HIGHS ZERO TO FIVE ABOVE IN MOST LOCATIONS. THIS ALONG
WITH DIMINISHING SURFACE WINDS SET THE STAGE FOR A CHILLY NIGHT
TUESDAY NIGHT WITH STILL -10 TO -15 IN OUTLYING LOCATIONS...NAMELY
NORTH CENTRAL IL. WITH THE DIMINISHING WINDS...FORECAST WIND CHILL
VALUES ARE FALLING OUT FOR LATE TUE NIGHT/WED MORNING AT -15 TO
-30 FROM SOUTH TO NORTH MOST OVER MOST OF THE AREA. THAT WOULD
TYPICALLY FALL MORE INTO THE WIND CHILL ADVISORY CRITERIA. HAVE
NOT MADE ANY ADJUSTMENTS TO THE HEADLINE TO GIVE THE NEXT SHIFT A
CHANCE TO LOOK FURTHER...BUT THAT DOWNGRADE FOR THE TAIL END OF
THE WARNING COULD HAPPEN WITH FUTURE SHIFTS FOR AT LEAST A
PORTION OF THE WARNING FOR TUE NIGHT/WED MORNING. 

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