166
FOUS11 KWBC 201933
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 PM EST MON JAN 20 2025
VALID 00Z TUE JAN 21 2025 - 00Z FRI JAN 24 2025
..GREAT LAKES
DAYS 1-2...
A LARGE CYCLONIC GYRE ENCOMPASSING MUCH OF THE EASTERN 2/3 OF THE
CONUS AND DRAPED FROM A MASSIVE UPPER LOW CENTERED OVER EASTERN
CANADA WILL MAINTAIN CAA ACROSS THE GREAT LAKES THROUGH THURSDAY,
WITH PERIODIC SHORTWAVE IMPULSES ROTATING THROUGH THE FLOW AND
OVERHEAD THE REGION. THE IMPRESSIVE UPPER LOW WILL MAINTAIN HEIGHT
ANOMALIES WELL BELOW NORMAL INTO THURSDAY, WITH PERSISTENT CAA
PUSHING W/NW FLOW ATOP THE GREAT LAKES. THE MOST IMPRESSIVE ASCENT
WILL ACCOMPANY A SHARP SHORTWAVE WHICH WILL CROSS THE REGION FROM
THE WEST TO EAST ON TUESDAY, DRIVING ENHANCED ASCENT THROUGH HEIGHT
FALLS AND STRONG PVA. THIS WILL ALSO RESULT IN ONE FINAL SUBSEQUENT
COLD SURGE REFLECTED BY 850MB TEMPS CRASHING TO AS LOW AS -20C TO
-30C OVER THE LAKES, COLDEST ACROSS THE U.P. OF MI.
THE CONTINUOUS CYCLONIC FLOW ALOFT WITH EMBEDDED SHORTWAVES WILL
RESULT IN A FAVORABLE ENVIRONMENT FOR ROUNDS OF LAKE EFFECT SNOW
(LES) IN THE FAVORED W/NW SNOW BELTS DOWNSTREAM OF ALL THE LAKES.
DESPITE LAKE SURFACE TEMPERATURES THAT HAVE COOLED DRAMATICALLY THE
PAST FEW WEEKS (NOW GENERALLY 0C TO +5C, WITH ICE PRESENT IN SOME
AREAS ACCORDING TO GLERL), THE EXTREME COLD AIR FUNNELING THROUGH
WILL PRODUCE STEEP LAPSE RATES, INVERSION DEPTHS TOWARDS 10,000
FT, AND LAKE-INDUCED INSTABILITY OF 500-1000 J/KG. THIS WILL
SUPPORT HEAVY BANDS OF LES, WITH SINGLE BANDS OFF OF LAKES ERIE AND
ONTARIO SUPPORTING 2-3"/HR RATES AT TIMES, AND 1"/HR RATES
ELSEWHERE. THE HEAVIEST AND MOST WIDESPREAD SNOW IS LIKELY D1 INTO
D2 BEHIND THE POTENT SHORTWAVE AND ACCOMPANYING WEAKENING FRONT,
AND COVERAGE/INTENSITY IS LIKELY TO WANE D2 INTO D3. HOWEVER, AT
LEAST MODEST LES IS PROGGED TO PERSIST INTO THE EARLY PART OF D3
ACROSS THE EASTERN LAKES.
2-DAY SNOWFALL PROBABILITIES FROM WPC ENDING 00Z/THURSDAY INDICATE
A HIGH CHANCE (>70%) FOR MORE THAN 8 INCHES FOR PORTIONS OF THE NW
L.P. OF MI, AS WELL AS DOWNSTREAM OF LAKES ERIE AND ONTARIO,
ESPECIALLY INTO THE CHAUTAUQUA RIDGE AND TUG HILL PLATEAU. THE
HEAVIEST SNOW TOTALS ARE LIKELY IN THE TUG HILL, HOWEVER, WHERE WPC
PROBABILITIES FOR MORE THAN 24 INCHES REACH 30-50%, AND LOCALLY 2-4
FEET OF SNOW IS POSSIBLE.
..TEXAS, GULF COAST, AND SOUTHEAST
DAYS 1-3...
...SIGNIFICANT, POTENTIALLY HISTORIC, WINTER STORM TO SPREAD ACROSS
THE GULF COAST AND PORTIONS OF THE SOUTHEAST THROUGH WEDNESDAY...
A RARE, POTENTIALLY HISTORIC, GULF-COAST AND SOUTHEAST ATLANTIC
COAST WINTER STORM BEGINS TONIGHT AND SPREAD ACROSS THE REGION
THROUGH WEDNESDAY. THE ANOMALOUS TO EXTREME COLD PLAGUING THE
EASTERN 2/3 OF THE CONUS WILL SET THE STAGE FOR THIS UPCOMING LOW
PRESSURE SYSTEM.
THE PRIMARY MECHANISM DRIVING THIS IMPRESSIVE EVENT WILL BE A
SHORTWAVE DIGGING ACROSS THE GREAT BASIN AND THEN
SHARPENING/INTENSIFYING AS IT PIVOTS TOWARDS THE GULF COAST
TUESDAY MORNING. THIS WILL INTERACT WITH A NORTHERN STREAM IMPULSE
TO PRODUCE A POSITIVELY TILTED FULL-LATITUDE TROUGH SURGING
EASTWARD THROUGH WEDNESDAY. DOWNSTREAM OF THIS AMPLIFICATION, A SW
TO NE ORIENTED JET STREAK WILL AMPLIFY TO ABOVE 150 KTS, LEAVING
ITS FAVORABLE DIFFLUENT RRQ ATOP THE GULF COAST, LEADING TO
PRONOUNCED DEEP LAYER ASCENT. AT THE SAME TIME, THE AFOREMENTIONED
GREAT BASIN SHORTWAVE WILL CONTINUE TO SHARPEN TO PRODUCE
IMPRESSIVE HEIGHT FALLS/PVA, OVERLAPPING WITH THE UPPER DIFFLUENCE
AND THE BAROCLINIC ZONE POSITIONED ACROSS THE GULF OF MEXICO TO
SPAWN A WAVE OF LOW PRESSURE MOVING EAST ACROSS IT.
DOWNSTREAM OF THIS DEVELOPING WAVE, MOISTURE ADVECTION WILL RAPIDLY
INTENSIFY ON 300K ISENTROPIC ASCENT AND ACCOMPANYING WAA, DRIVING
PWS NORTHWARD INTO THE GULF COAST AND SOUTHEAST, WITH PW ANOMALIES
APPROACHING +1 SIGMA TO FUEL WIDESPREAD AND EXPANDING
PRECIPITATION. WHILE THERE REMAINS SOME UNCERTAINTY AS FAR AS WHERE
THE MIXED PRECIP ZONE WILL OCCUR, THE GUIDANCE HAS CONTINUED TO
TREND A BIT FARTHER SOUTH/COLDER, SUGGESTING THAT EVEN THE
IMMEDIATE BEACHES FROM HOUSTON TO PANAMA CITY WILL EXPERIENCE
SNOWFALL. ADDITIONALLY, WITH EXTREMELY COLD AND DRY AIR POSITIONED
JUST TO THE NORTH, AND LOW-LEVEL NORTHERLY FLOW AGEOSTROPHICALLY
ENHANCING THE LOW-LEVEL BAROCLINIC GRADIENT, SOME INCREASED FGEN IS
EXPECTED FROM EASTERN TX THROUGH THE FL PANHANDLE. THIS WILL BE
ENHANCED BY THE RESPONSE TO THE UPPER JET ALOFT, AND THE WPC
PROTOTYPE SNOWBAND TOOL INDICATES A HIGH CHANCE FOR 1+"/HR SNOW
RATES FROM NEAR HOUSTON TO MOBILE BAY DESPITE AN ELEVATED DGZ. THIS
COULD ADDITIONALLY COOL THE COLUMN CAUSING THE MIXED PRECIP ZONE TO
PUSH EVEN FARTHER SOUTH. THESE TYPES OF SNOW RATES IN AREAS THAT DO
NOT TYPICALLY RECEIVE THEM WILL CREATE MAJOR TO EXTREME IMPACTS,
AND HISTORIC SNOWFALL IS POSSIBLE ACROSS THIS AREA. WPC
PROBABILITIES ARE MODERATE TO HIGH (50-70%) FOR MORE THAN 4 INCHES
ON D1 FROM NEAR BEAUMONT, TX THROUGH SOUTHERN LA, WITH LOCALLY MORE
THAN 6 INCHES POSSIBLE (30% CHANCE) WHERE THE MOST INTENSE BANDING
OCCURS. SURROUNDING THIS REGION, THERE EXISTS A BROAD MODERATE
CHANCE (30-70%) FOR MORE THAN 2 INCHES FROM EAST-CENTRAL TX THROUGH
THE NW FLORIDA PANHANDLE.
FARTHER EAST INTO GEORGIA, THE NORTHERN FLORIDA PENINSULA, AND THE
CAROLINAS, THE GUIDANCE HAS BEEN FLIP-FLOPPING AS FAR AS THE
NORTHERN EXTENT OF MOISTURE. HOWEVER, TODAY'S RUNS HAVE PUSHED THE
MOISTURE A BIT FARTHER NORTH DESPITE THE DRY/COLD AIRMASS
POSITIONED TO THE NORTH, SO EVEN THESE AREAS MAY SEE RARE
SIGNIFICANT SNOWFALL ACCUMULATIONS, DESPITE MORE MODEST RATES
OVERALL. IN THIS REGION, AND GENERALLY ON D2, WPC PROBABILITIES FOR
MORE THAN 2 INCHES ARE 30-50% FROM SOUTHERN AL AND SOUTH-CENTRAL GA
EASTWARD TO CAPE FEAR AND THE OUTER BANKS OF NC.
FINALLY, ACROSS PORTIONS OF SOUTH TEXAS, AND AREAS FROM THE FL
PANHANDLE TO THE NORTHERN FL PENINSULA, A MIXED ZONE OF SNOW,
SLEET, AND FREEZING RAIN IS LIKELY. THERE CONTINUES TO BE
UNCERTAINTY IN THE LATITUDINAL PLACEMENT OF THE HEAVIEST FREEZING
RAIN/ICING AMOUNTS, BUT CURRENT WPC PROBABILITIES FOR AT LEAST 0.1"
OF ICE ARE AS HIGH AS 30% IN SOUTH TEXAS, AND 50-70% ACROSS THE
NORTHERN FL PENINSULA, WHERE LOCALLY MORE THAN 0.25" OF ICE IS
POSSIBLE.
THIS EVENT HAS PROMPTED THE ISSUANCE OF COLLABORATED KEY MESSAGES
(KEYMESSAGE_1) LINKED BELOW.
WEISS
...WINTER STORM KEY MESSAGES ARE IN EFFECT. PLEASE SEE CURRENT
KEY MESSAGES BELOW...
HTTPS://WWW.WPC.NCEP.NOAA.GOV/KEY_MESSAGES/LATESTKEYMESSAGE_1.PNG
HTTPS://WWW.WPC.NCEP.NOAA.GOV/KEY_MESSAGES/LATESTKEYMESSAGE_2.PNG
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