Post by rocket on Jan 25, 2014 15:30:52 GMT -6
This time this storm will be coming from the southwest instead of the northwest..
000
FXUS63 KLOT 252120
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
320 PM CST SAT JAN 25 2014
.DISCUSSION...
318 PM CST
THE MAIN CONCERNS TODAY CONTINUE TO BE PLENTIFUL...AND INCLUDE THE
QUICK HITTING MODERATE TO HEAVY SNOW EVENT TONIGHT INTO EARLY SUNDAY
MORNING...THE GOOD POTENTIAL FOR SIGNIFICANT BLOWING AND DRIFTING
SNOW LATE SUNDAY AND SUNDAY NIGHT...AND FINALLY THE LIFE THREATENING
WIND CHILLS EARLY NEXT WEEK.
HEADLINE OVERVIEW:
...HAVE UPGRADED THE WIND CHILL WATCH TO WARNING FOR WIND CHILLS IN
EXCESS OF 40 BELOW BY MONDAY NIGHT.
...ALSO HAVE ISSUED A WINTER WEATHER ADVISORY FROM LATE TONIGHT
THROUGH EARLY MONDAY FOR SNOW TONIGHT AND SIGNIFICANT BLOWING AND
DRIFTING SNOW SUNDAY NIGHT.
AFTER OUR QUICK HIT OF LIGHT SNOW LAST NIGHT...WINDS CONTINUE TO BE
GUSTY OUT OF THE NORTHWEST IN THE WAKE OF THE FIRST COLD FRONT. THIS
IS LIKELY PRODUCING SOME BLOWING SNOW IN THE OPEN AREAS. THESE WINDS
WILL CONTINUE TO ABATE THROUGH THE EVENING AND ACTUALLY BEGIN TO
BACK OUT OF THE SOUTH-SOUTHEAST OVERNIGHT AHEAD OF THE NEXT CLIPPER
SYSTEM.
WATER VAPOR IMAGERY EARLY THIS AFTERNOON SHOWS OUR NEXT DISTURBANCE
NOW DROPPING SOUTHWARD ACROSS SASKATCHEWAN AND THIS IS ALREADY
PRODUCING A GOOD AREA OF SNOWFALL ACROSS PORTIONS OF THE DAKOTAS
EARLY THIS AFTERNOON. THIS CLIPPER IS STILL FORECAST TO RACE
SOUTHEASTWARD ACROSS NORTHERN ILLINOIS BY SUNDAY MORNING. ALTHOUGH
THE SURFACE LOW WILL BE WEAKENING AS IT ARRIVES...IT WILL BE
TRACKING ALONG A STOUT BAROCLINIC ZONE. THIS WILL ALLOW FOR A STRONG
BAND OF FRONTOGENESIS TO SET UP ALONG AND JUST TO THE NORTH OF THE
TRACK OF THE SURFACE LOW....WHICH SHOULD BE RIGHT ACROSS THE CENTRAL
OF MY CWA.
ISENTROPIC ASCENT WILL RAMP UP QUICKLY ACROSS THE AREA AFTER
MIDNIGHT TONIGHT. THE 285K SURFACE SUGGESTS WINDS IN EXCESS OF 50
KT AT A SHARP ANGLE TO THE PRESSURE CONTOURS TOWARDS
MORNING...RESULTING IN STRONG ISENTROPIC ASCENT...AND A RAPID
MOISTENING OF THE COLUMN. THIS SAME ISENTROPIC SURFACE...WHICH
BISECTS THE 700 MB PRESSURE SURFACE...ALSO IS PROGGED TO HAVE A
MIXING RATIO OF NEARLY 2.5 G/KG. USING THE GARCIA METHOD...THIS
WOULD SUGGEST SNOW AMOUNTS UP TO 5 INCHES ACROSS PORTIONS OF THE
AREA.
OVERALL...ALTHOUGH THIS WILL BE A FAST MOVING HIT OF SNOW ACROSS THE
AREA...THE STRONG DYNAMIC FORCING WILL LIKELY RESULT IN A WINDOW OF
MODERATE TO EVEN HEAVY SNOW EARLY SUNDAY MORNING. OVERALL...THIS
STILL APPEARS TO BE A 2 TO 4 INCH EVENT FOR MOST AREAS.
HOWEVER...THE STRONG FORCING FOR ASCENT COULD EASILY PRODUCE SNOW
RATES UP TO AN INCH PER HOUR...AND PRODUCE UP TO 4 TO 5
INCHES IN SOME AREAS WITHIN ONLY A 4 TO 5 HOUR PERIOD. IT CURRENTLY
APPEARS THAT THE HEAVIEST BAND OF SNOW OF 3 TO 5 INCHES MAY FALL
FROM AROUND DIXON EAST-SOUTHEASTWARD TOWARDS THE JOLIET AREA...WITH
2 TO 4 INCHES ARE EXPECTED ELSEWHERE. TO OBTAIN THESE SNOW AMOUNTS I
FOLLOWED CLOSE TO A 15-20 TO 1 RATIO NORTH...WHERE THE DGZ WILL BE
THE DEEPEST...AND A 12-15 TO 1 ACROSS THE FAR SOUTH.
THE SNOW SHOULD ONSET AROUND 1 OR 2 AM ACROSS NORTH CENTRAL ILLINOIS
AND AROUND 3 AM IN THE CHICAGO AREA....AND LAST THROUGH MID
MORNING...BEFORE DRIER AIR SHIFTS ACROSS THE REGION IN THE MID
LEVELS. GIVEN THAT THE SNOW WILL FALL AT A RAPID RATE...I HAVE
CHOSEN TO ISSUE AN WINTER WEATHER ADVISORY FOR THE ENTIRE AREA FOR
2 TO 5 INCHES OF SNOW.
ONCE THE SNOW ENDS SUNDAY MORNING...THERE COULD BE SOME LINGERING
DRIZZLE OR FREEZING DRIZZLE ACROSS MY SOUTHEASTERN COUNTIES. MODEL
BUFFER SOUNDINGS SUGGEST THAT THE LOWER LEVELS WILL REMAIN
SATURATED BELOW THE DGZ...AND HENCE THE CLOUDS COULD BECOME VOID OF
ICE CRYSTALS SETTING UP DRIZZLE. IN SPITE OF THIS POTENTIAL...I HAVE
CHOSEN TO LEAVE THE MENTION OUT OF THE FORECAST FOR NOW...DUE TO
ITS LIKELIHOOD OF BEING SHORT LIVED.
ALTHOUGH THE AFTERNOON MAY BE QUIET FOR A PERIOD...AFTER THE PRECIP
ABATES...I HAVE CHOSEN TO KEEP THE WINTER WEATHER ADVISORY GOING
THROUGH SUNDAY NIGHT. THE REASON FOR DOING THIS IS BECAUSE A STRONG
ARCTIC FRONT IS SET TO DROP ACROSS THE AREA BY LATE AFTERNOON OR VERY
EARLY SUNDAY EVENING. ONCE THIS FRONT MOVES THROUGH...STRONG
PRESSURE RISES WILL OVERSPREAD THE AREA AS SURFACE HIGH PRESSURE
BEGINS TO BUILD IN ACROSS THE NORTHERN PLAINS. THIS WILL SET THE
STAGE FOR A PERIOD OF STRONG NORTHWESTERLY WINDS OF 20 TO 35 MPH
WITH GUSTS UP TO 45 MPH SUNDAY NIGHT. THE MAIN CONCERN WITH THESE
WINDS WILL BE THE POTENTIAL FOR NEAR BLIZZARD CONDITIONS TO DEVELOP
ACROSS THE AREA AS THE NEWLY FALLEN DRY SNOW GETS BLOWN AROUND.
IT ALSO APPEARS POSSIBLE THAT ADDITIONAL SHOW SHOWERS WILL BE
OCCURRING SUNDAY EVENING WITH THE STRONG WINDS. LOW LEVEL LAPSE RATES
ARE EXPECTED TO INCREASE AS ANOTHER MID LEVEL SHORT WAVE/PV ANOMALY
DROPS ACROSS THE AREA. THIS COULD RESULT IN SOME ADDITIONAL
LIGHT ACCUMULATIONS. HOWEVER...THE POTENTIAL FOR FALLING SNOW IN
CONJUNCTION WITH SIGNIFICANT BLOWING AND DRIFTING SNOW COULD RESULT IN
BETTER CHANCES FOR NEAR BLIZZARD CONDITIONS. AT THE PRESENT...I HAVE
CHOSEN TO COVER THIS THREAT WITH THE WINTER WEATHER ADVISORY...DUE
TO UNCERTAINTIES ON HOW LOW VISIBILITIES WILL BECOME AND HOW MUCH
ADDITIONAL SNOW WILL FALL DURING THIS TIME. IF IT APPEARS THAT A DECENT
AMOUNT OF SNOW FALLS WITH THE STRONG WINDS SUNDAY EVENING...IT MAY
BE NECESSARY TO UPGRADE THE ADVISORY TO EITHER A WINTER STORM OR
BLIZZARD WARNING.
OTHERWISE...THE MAIN STORY WILL BE SWITCHING TO THE LIFE THREATENING
COLD AND WIND CHILLS. DUE TO ACTUAL AIR TEMPERATURES DROPPING BELOW
ZERO BY MONDAY MORNING...WIND CHILLS WILL EASILY FALL TO AND BELOW
30 BELOW RESULTING IN WIND CHILL WARNING WIND CHILLS. THIS DANGEROUS
COLD SHOULD PEAK MONDAY NIGHT...AS THE SURFACE HIGH SHIFTS ACROSS
WEST CENTRAL ILLINOIS. THIS COULD ALLOW THE WINDS TO DROP OFF SOME
MONDAY NIGHT...BUT THIS WILL ALSO ALLOW TEMPS TO DROP POTENTIALLY
INTO THE 20S BELOW ZERO...WHICH WOULD BREAK OR TIE TEMPERATURE
RECORDS. SEE CLIMO SECTION BELOW.
THINGS WILL BEGIN TO MODERATE LATER IN THE WEEK...BUT TEMPERATURES
WILL STILL LIKELY REMAIN BELOW AVERAGE. ADDITIONAL CHANCES FOR SNOW
ALSO LOOK TO COME INTO PLAY AGAIN LATER IN THE WEEK. HIGH LATITUDE
BLOCKING ACROSS ALASKA ASSOCIATED WITH A -EPO AND THE PROSPECTS FOR
AN EVOLVING -PNA PATTERN ACROSS THE CONUS COULD SET THE STAGE FOR A
MORE POTENT SOUTHWESTERN STORM PATTERN ACROSS THE CENTRAL CONUS INTO
NEXT WEEKEND.
www.nws.noaa.gov/view/prodsByState.php?state=IL&prodtype=discussion
000
FXUS63 KLOT 252120
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
320 PM CST SAT JAN 25 2014
.DISCUSSION...
318 PM CST
THE MAIN CONCERNS TODAY CONTINUE TO BE PLENTIFUL...AND INCLUDE THE
QUICK HITTING MODERATE TO HEAVY SNOW EVENT TONIGHT INTO EARLY SUNDAY
MORNING...THE GOOD POTENTIAL FOR SIGNIFICANT BLOWING AND DRIFTING
SNOW LATE SUNDAY AND SUNDAY NIGHT...AND FINALLY THE LIFE THREATENING
WIND CHILLS EARLY NEXT WEEK.
HEADLINE OVERVIEW:
...HAVE UPGRADED THE WIND CHILL WATCH TO WARNING FOR WIND CHILLS IN
EXCESS OF 40 BELOW BY MONDAY NIGHT.
...ALSO HAVE ISSUED A WINTER WEATHER ADVISORY FROM LATE TONIGHT
THROUGH EARLY MONDAY FOR SNOW TONIGHT AND SIGNIFICANT BLOWING AND
DRIFTING SNOW SUNDAY NIGHT.
AFTER OUR QUICK HIT OF LIGHT SNOW LAST NIGHT...WINDS CONTINUE TO BE
GUSTY OUT OF THE NORTHWEST IN THE WAKE OF THE FIRST COLD FRONT. THIS
IS LIKELY PRODUCING SOME BLOWING SNOW IN THE OPEN AREAS. THESE WINDS
WILL CONTINUE TO ABATE THROUGH THE EVENING AND ACTUALLY BEGIN TO
BACK OUT OF THE SOUTH-SOUTHEAST OVERNIGHT AHEAD OF THE NEXT CLIPPER
SYSTEM.
WATER VAPOR IMAGERY EARLY THIS AFTERNOON SHOWS OUR NEXT DISTURBANCE
NOW DROPPING SOUTHWARD ACROSS SASKATCHEWAN AND THIS IS ALREADY
PRODUCING A GOOD AREA OF SNOWFALL ACROSS PORTIONS OF THE DAKOTAS
EARLY THIS AFTERNOON. THIS CLIPPER IS STILL FORECAST TO RACE
SOUTHEASTWARD ACROSS NORTHERN ILLINOIS BY SUNDAY MORNING. ALTHOUGH
THE SURFACE LOW WILL BE WEAKENING AS IT ARRIVES...IT WILL BE
TRACKING ALONG A STOUT BAROCLINIC ZONE. THIS WILL ALLOW FOR A STRONG
BAND OF FRONTOGENESIS TO SET UP ALONG AND JUST TO THE NORTH OF THE
TRACK OF THE SURFACE LOW....WHICH SHOULD BE RIGHT ACROSS THE CENTRAL
OF MY CWA.
ISENTROPIC ASCENT WILL RAMP UP QUICKLY ACROSS THE AREA AFTER
MIDNIGHT TONIGHT. THE 285K SURFACE SUGGESTS WINDS IN EXCESS OF 50
KT AT A SHARP ANGLE TO THE PRESSURE CONTOURS TOWARDS
MORNING...RESULTING IN STRONG ISENTROPIC ASCENT...AND A RAPID
MOISTENING OF THE COLUMN. THIS SAME ISENTROPIC SURFACE...WHICH
BISECTS THE 700 MB PRESSURE SURFACE...ALSO IS PROGGED TO HAVE A
MIXING RATIO OF NEARLY 2.5 G/KG. USING THE GARCIA METHOD...THIS
WOULD SUGGEST SNOW AMOUNTS UP TO 5 INCHES ACROSS PORTIONS OF THE
AREA.
OVERALL...ALTHOUGH THIS WILL BE A FAST MOVING HIT OF SNOW ACROSS THE
AREA...THE STRONG DYNAMIC FORCING WILL LIKELY RESULT IN A WINDOW OF
MODERATE TO EVEN HEAVY SNOW EARLY SUNDAY MORNING. OVERALL...THIS
STILL APPEARS TO BE A 2 TO 4 INCH EVENT FOR MOST AREAS.
HOWEVER...THE STRONG FORCING FOR ASCENT COULD EASILY PRODUCE SNOW
RATES UP TO AN INCH PER HOUR...AND PRODUCE UP TO 4 TO 5
INCHES IN SOME AREAS WITHIN ONLY A 4 TO 5 HOUR PERIOD. IT CURRENTLY
APPEARS THAT THE HEAVIEST BAND OF SNOW OF 3 TO 5 INCHES MAY FALL
FROM AROUND DIXON EAST-SOUTHEASTWARD TOWARDS THE JOLIET AREA...WITH
2 TO 4 INCHES ARE EXPECTED ELSEWHERE. TO OBTAIN THESE SNOW AMOUNTS I
FOLLOWED CLOSE TO A 15-20 TO 1 RATIO NORTH...WHERE THE DGZ WILL BE
THE DEEPEST...AND A 12-15 TO 1 ACROSS THE FAR SOUTH.
THE SNOW SHOULD ONSET AROUND 1 OR 2 AM ACROSS NORTH CENTRAL ILLINOIS
AND AROUND 3 AM IN THE CHICAGO AREA....AND LAST THROUGH MID
MORNING...BEFORE DRIER AIR SHIFTS ACROSS THE REGION IN THE MID
LEVELS. GIVEN THAT THE SNOW WILL FALL AT A RAPID RATE...I HAVE
CHOSEN TO ISSUE AN WINTER WEATHER ADVISORY FOR THE ENTIRE AREA FOR
2 TO 5 INCHES OF SNOW.
ONCE THE SNOW ENDS SUNDAY MORNING...THERE COULD BE SOME LINGERING
DRIZZLE OR FREEZING DRIZZLE ACROSS MY SOUTHEASTERN COUNTIES. MODEL
BUFFER SOUNDINGS SUGGEST THAT THE LOWER LEVELS WILL REMAIN
SATURATED BELOW THE DGZ...AND HENCE THE CLOUDS COULD BECOME VOID OF
ICE CRYSTALS SETTING UP DRIZZLE. IN SPITE OF THIS POTENTIAL...I HAVE
CHOSEN TO LEAVE THE MENTION OUT OF THE FORECAST FOR NOW...DUE TO
ITS LIKELIHOOD OF BEING SHORT LIVED.
ALTHOUGH THE AFTERNOON MAY BE QUIET FOR A PERIOD...AFTER THE PRECIP
ABATES...I HAVE CHOSEN TO KEEP THE WINTER WEATHER ADVISORY GOING
THROUGH SUNDAY NIGHT. THE REASON FOR DOING THIS IS BECAUSE A STRONG
ARCTIC FRONT IS SET TO DROP ACROSS THE AREA BY LATE AFTERNOON OR VERY
EARLY SUNDAY EVENING. ONCE THIS FRONT MOVES THROUGH...STRONG
PRESSURE RISES WILL OVERSPREAD THE AREA AS SURFACE HIGH PRESSURE
BEGINS TO BUILD IN ACROSS THE NORTHERN PLAINS. THIS WILL SET THE
STAGE FOR A PERIOD OF STRONG NORTHWESTERLY WINDS OF 20 TO 35 MPH
WITH GUSTS UP TO 45 MPH SUNDAY NIGHT. THE MAIN CONCERN WITH THESE
WINDS WILL BE THE POTENTIAL FOR NEAR BLIZZARD CONDITIONS TO DEVELOP
ACROSS THE AREA AS THE NEWLY FALLEN DRY SNOW GETS BLOWN AROUND.
IT ALSO APPEARS POSSIBLE THAT ADDITIONAL SHOW SHOWERS WILL BE
OCCURRING SUNDAY EVENING WITH THE STRONG WINDS. LOW LEVEL LAPSE RATES
ARE EXPECTED TO INCREASE AS ANOTHER MID LEVEL SHORT WAVE/PV ANOMALY
DROPS ACROSS THE AREA. THIS COULD RESULT IN SOME ADDITIONAL
LIGHT ACCUMULATIONS. HOWEVER...THE POTENTIAL FOR FALLING SNOW IN
CONJUNCTION WITH SIGNIFICANT BLOWING AND DRIFTING SNOW COULD RESULT IN
BETTER CHANCES FOR NEAR BLIZZARD CONDITIONS. AT THE PRESENT...I HAVE
CHOSEN TO COVER THIS THREAT WITH THE WINTER WEATHER ADVISORY...DUE
TO UNCERTAINTIES ON HOW LOW VISIBILITIES WILL BECOME AND HOW MUCH
ADDITIONAL SNOW WILL FALL DURING THIS TIME. IF IT APPEARS THAT A DECENT
AMOUNT OF SNOW FALLS WITH THE STRONG WINDS SUNDAY EVENING...IT MAY
BE NECESSARY TO UPGRADE THE ADVISORY TO EITHER A WINTER STORM OR
BLIZZARD WARNING.
OTHERWISE...THE MAIN STORY WILL BE SWITCHING TO THE LIFE THREATENING
COLD AND WIND CHILLS. DUE TO ACTUAL AIR TEMPERATURES DROPPING BELOW
ZERO BY MONDAY MORNING...WIND CHILLS WILL EASILY FALL TO AND BELOW
30 BELOW RESULTING IN WIND CHILL WARNING WIND CHILLS. THIS DANGEROUS
COLD SHOULD PEAK MONDAY NIGHT...AS THE SURFACE HIGH SHIFTS ACROSS
WEST CENTRAL ILLINOIS. THIS COULD ALLOW THE WINDS TO DROP OFF SOME
MONDAY NIGHT...BUT THIS WILL ALSO ALLOW TEMPS TO DROP POTENTIALLY
INTO THE 20S BELOW ZERO...WHICH WOULD BREAK OR TIE TEMPERATURE
RECORDS. SEE CLIMO SECTION BELOW.
THINGS WILL BEGIN TO MODERATE LATER IN THE WEEK...BUT TEMPERATURES
WILL STILL LIKELY REMAIN BELOW AVERAGE. ADDITIONAL CHANCES FOR SNOW
ALSO LOOK TO COME INTO PLAY AGAIN LATER IN THE WEEK. HIGH LATITUDE
BLOCKING ACROSS ALASKA ASSOCIATED WITH A -EPO AND THE PROSPECTS FOR
AN EVOLVING -PNA PATTERN ACROSS THE CONUS COULD SET THE STAGE FOR A
MORE POTENT SOUTHWESTERN STORM PATTERN ACROSS THE CENTRAL CONUS INTO
NEXT WEEKEND.
www.nws.noaa.gov/view/prodsByState.php?state=IL&prodtype=discussion