Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 212315
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
515 PM CST WED JAN 21 2015

.SHORT TERM...(TONIGHT AND THURSDAY)
ISSUED AT 200 PM CST WED JAN 21 2015

BAND OF LIGHT SNOW CONTINUES TO SAG SOUTH/SOUTHEAST THIS
AFTERNOON...ASSOCIATED WITH A SFC TROUGH/FRONTOGENETIC FORCING. THE
TRENDS FAVOR A DECREASE IN AREAL COVERAGE AND INTENSITY. LITTLE IF
ANY ADDITIONAL ACCUMULATIONS ARE EXPECTED FOR THE REST OF THE
AFTERNOON-EARLY EVENING. THAT SAID...THE LIGHT SNOW DOES LOOK LIKE
IT COULD PERSISTING INTO THE EARLY EVENING...SO HAVE EXTENDED SMALL
CHANCES SOUTH OF I-90.

HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST ON THURSDAY...WHICH
SHOULD RESULT IN A GRADUAL CLEARING OF THE CLOUDS FROM NORTHWEST TO
SOUTHEAST.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 200 PM CST WED JAN 21 2015

THE OVERALL PATTERN VIA THE GFS AND ECMWF FOR THE WEEKEND INTO NEXT
WEEK IS BUILDING AN UPPER LEVEL RIDGE TO THE WEST...KEEPING THE
UPPER MISSISSIPPI RIVER VALLEY UNDER NORTHWEST FLOW. POSITIVE
HEIGHT/TEMP ANOMALIES BUILD ACROSS THE PLAIN STATES BY EARLY NEXT
WEEK...BUT HOLD TO THE WEST. ANY SIGNIFICANT WARMING SHOULD THUS
STAY WEST THROUGH THIS PERIOD...BUT STILL EXPECT THE AT OR ABOVE
NORMAL TREND FOR TEMPS TO CONTINUE LOCALLY.

THE NORTHWEST FLOW WILL SLIDE VARIOUS PERTURBATIONS ALONG IT...WITH
MOST OF THIS ACTIVITY HOLDING NORTH OF THE LOCAL AREA.
HOWEVER...THERE IS ONE SHORTWAVE OF INTEREST THAT IS CURRENTLY
SLATED TO TAKE AIM ON THE REGION SAT NIGHT THROUGH SUNDAY. A HEFTY
QG CONVERGENT SIGNAL THROUGH THE LAYERS ACCOMPANIES THE
SHORTWAVE...ALONG WITH A DECENT AMOUNT OF ISENTROPIC UPGLIDE ON THE
280-295 K SFCS. NOT A DEEP DENDRITIC LAYER CURRENTLY INDICATED VIA
THE SREF OR GFS BUFKIT SOUNDINGS...AND SNOW OUTPUT IN THE COBB HAS
VARIED QUITE A BIT. THAT SAID...THE MODELS SUGGEST THE SHORTWAVE
WILL PACK A BIT OF A PUNCH...AND THERE WILL BE SATURATION TO WORK
WITH. SEE THE POTENTIAL FOR 1 TO 4 INCHES AT THIS MOMENT...WITH THE
HIGHER AMOUNTS FAVORED EAST OF THE MISSISSIPPI /I-94 CORRIDOR/.
OBVIOUSLY...A BIT TOO EARLY TO TRY AND REFINE WHERE THE BEST SNOW
CHANCES/AMOUNTS WILL LIE...BUT ITS A SYSTEM THAT COULD REQUIRE
ADVISORIES AND BEARS WATCHING.

MOVING BACK IN TIME...THERE IS A WEAK SHORTWAVE SLATED TO SPIN
ACROSS NORTHERN PARTS OF THE REGION FRI/FRI NIGHT. THE BULK OF THE
UPPER LEVEL FORCING WILL HOLD TO THE NORTH/NORTHEAST...BUT THE
SYSTEM WILL DRAG A SFC FRONT ACROSS THE LOCAL AREA. SOME MEAGER
FRONTOGENETIC FORCING AROUND IT...ALONG WITH QG CONVERGENCE. THE
BETTER FORCING/DEEPER SATURATION WOULD DICTATE THE BEST PCPN ACROSS
NORTHERN WI...BUT LIKELY ENOUGH SOUTHWEST OF THERE FOR SMALL
CHANCES. WHAT WOULD/COULD FALL IS IN QUESTION AS BUFKIT SOUNDINGS
SUGGEST SATURATION WOULD BE SHALLOW...ENOUGH SO THAT ICE MIGHT NOT
BE IN THE CLOUD LAYER. IN ADDITION...AIR TEMPS SHOULD BE ABOVE
FREEZING DURING THE DAY...AND MANY ROADS AS WELL. WILL GO WITH A MIX
OF DRIZZLE/SNOW...AND SOME POTENTIAL FOR FREEZING.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 515 PM CST WED JAN 21 2015

SNOW IS FINALLY COMING TO AN END AT THE TAF SITES WITH THE BACK
EDGE RAPIDLY APPROACHING I-90 FROM THE NORTH. WITH THE EXITING
SNOW...VISIBILITIES WILL IMPROVE TO VFR WITHIN THE NEXT 1-2 HOURS.
EXPECT DRY WEATHER FOR THE REST OF THE PERIOD...HOWEVER...WHEN THE
STRATUS CAN CLEAR IS THE NEXT BIG QUESTION. CEILINGS ARE PRESENTLY
MVFR...BUT COULD FALL A FEW HUNDRED FEET PLACING RST INTO IFR OVER
THE NEXT FEW HOURS WITH LOSS OF DAYTIME HEATING. A SURFACE RIDGE
OVER NORTH DAKOTA WHERE CEILINGS ARE VFR IS FORECAST TO CROSS THE
TAF SITES THURSDAY AFTERNOON...SWINGING WINDS AROUND TO THE
SOUTHWEST. HAVE PUT IN 20Z AS AN APPROXIMATE TIME WHEN THE LOW
CLOUDS CAN SCATTER OUT...RELATED TO THE TIMING OF THE HIGH
PRESSURE RIDGE CROSSING...BUT THIS MAY NEED ADJUSTMENT AS WE GET
CLOSER.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...AJ


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