559
FXUS63 KARX 121955
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
255 PM CDT SUN JUL 12 2020
SHORT TERM
(THIS EVENING THROUGH MONDAY)
ISSUED AT 245 PM CDT SUN JUL 12 2020
EARLY AFTERNOON ANALYSIS SHOWED UPPER LEVEL RIDGING STARTING TO
WORK IN FROM THE WEST, WITH PLENTY OF CUMULUS CLOUDS AROUND THE
REGION. WATER VAPOR IMAGERY DID SHOW A VERY WEAK WAVE SLIDING
THROUGH AREAS EAST OF THE MISSISSIPPI RIVER AND MODEL SOUNDINGS
INDICATED A BIT OF INSTABILITY IN THE CUMULUS LAYER, SO COULD SEE
A FEW ISOLATED SHOWERS DEVELOP. HOWEVER, WITH A STOUT CAP RIGHT
ABOVE THE CUMULUS LAYER, THE RIDGING BUILDING IN, AND FAIRLY DRY
AIR, WOULD EXPECT THOSE TO BE FEW AND FAR BETWEEN IF THEY DEVELOP
AT ALL.
TONIGHT, COULD SEE SOME PATCHY FOG AROUND THE AREA GIVEN MOSTLY
CLEAR SKIES AND LIGHT WINDS FOR A BULK OF THE NIGHT, THOUGH A
TIGHTER PRESSURE GRADIENT WILL BE BUILDING IN FROM THE WEST.
OTHERWISE, LOW TEMPERATURES WILL BE IN THE 50S TO LOWER 60S.
UPPER LEVEL RIDGING WILL BE IN PLACE OVER THE FORECAST AREA ON
MONDAY, LEADING TO ANOTHER SEASONABLE AND MAINLY DRY DAY. LIKE
SUNDAY, COULD SEE A FEW POP UP SHOWERS WITH A BIT OF INSTABILITY IN
THE CUMULUS LAYER PER SOME MODEL SOUNDINGS. OTHERWISE, THE
AFOREMENTIONED PRESSURE GRADIENT WILL LEAD TO STRENGTHENING
SOUTHERLY FLOW AHEAD OF A LOW PRESSURE SYSTEM AND COLD FRONT SLIDING
THROUGH THE NORTHERN PLAINS. PER THE 12.15Z RAP, SOME RAIN AHEAD OF
THE FRONT COULD SNEAK INTO THE FORECAST AREA BY LATE MONDAY
AFTERNOON, THOUGH GENERAL MODEL CONSENSUS WOULD FAVOR ANY
PRECIPITATION HOLDING OFF UNTIL LATER.
LONG TERM
(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 245 PM CDT SUN JUL 12 2020
WE'VE HAD QUITE THE AIRMASS EXCHANGE WITH DEWPOINTS ONLY IN THE
50S TO LOWER 60S MOST LOCATIONS. DEWPOINTS WILL MOSTLY REMAIN IN
THE 50S AND 60S, HOWEVER AS WE MOVE TOWARD THE WEEKEND, LOOK FOR
THE DEWPOINTS TO CLIMB INTO THE 70S. TUESDAY LOOKS LIKE THE
COOLEST DAY AND SATURDAY THE WARMEST/MUGGY. MOST TEMPERATURES
SHOULD REACH THE HIGHS IN THE 80S, BUT READINGS WILL BE HELD TO
THE 70S TUESDAY AND THERE SHOULD BE QUITE A FEW 90S SATURDAY AND A
FEW STILL SUNDAY DEPENDING ON WHERE THE SURFACE FRONT IS.
AN 80KT 300MB JET WILL MOVE ON TO THE WASHINGTON/OREGON COAST SUNDAY
NIGHT AND TRAVERSE ACROSS THE NORTHERN ROCKIES AND THE NORTHERN
PLAINS INTO MINNESOTA BY TUESDAY NIGHT. THE 500MB PATTERN HAS A MID-
TROPOSPHERIC RIDGE FROM MINNESOTA THROUGH THE CENTRAL PLAINS. THE
500MB TROUGH EXTENDS INTO THE NORTHWEST PART OF THE U.S. FROM A
CLOSED LOW PRESSURE SYSTEM OVER SASKATCHEWAN FLATTENS THE RIDGE
MONDAY WITH A BROAD TROUGH THROUGH TUESDAY NIGHT. THE BROAD TROUGH
REMAINS IN PLACE WITH SOME SLIGHT RIDGING OVER THE WESTERN HIGH
PLAINS THURSDAY. THE STRONGER SHORTWAVE ENERGY TRACKS ACROSS
SOUTHERN CANADA WITH A RIPPLY ZONAL FLOW ACROSS THE NORTHERN U.S.
FRIDAY THROUGH SUNDAY. MEANWHILE...THE SOUTHERN PLAINS REMAINS
UNDER THE INFLUENCE OF A LARGE HIGH PRESSURE SYSTEM.
A COLD FRONT WILL APPROACH MONDAY NIGHT WITH SOME SPOTTY PRE-
FRONTAL CONVECTION POSSIBLE, INCREASING BY TUESDAY MORNING.
SHOWERS AND THUNDERSTORMS BECOME MORE WIDESPREAD ALONG THE FRONT
AS IT SAGS SOUTHWARD TUESDAY AND PUSHES THROUGH THE AREA TUESDAY
NIGHT. THERE IS A SEVERE WEATHER THREAT AND POTENTIAL FOR HEAVY
RAIN TUESDAY AND TUESDAY EVENING. PRECIPITABLE WATER VALUES
INCREASE TO 1.5 TO 2 INCHES WITH WARM CLOUD DEPTHS NEAR 4KM. THE
STORMS THAT DEVELOP WILL BE CAPABLE OF PUTTING DOWN HEAVY RAIN AND
WITH A FRONT IN THE AREA, INCREASE THE PROBABILITY OF TRAINING.
RELATED TO SEVERE STORMS, INSTABILITY IS MARGINAL...1000-2000J/KG,
HOWEVER THERE IS INCREASING SHEAR, BOTH 0-6KM SHEAR AND 0-3KM
SHEAR DURING THE AFTERNOON AND EVENING AS A SHORTWAVE ROUNDS THE
BASE OF THE LARGER SCALE TROUGH. FORECAST SOUNDINGS SHOW MODEST
LAPSE RATES. THE MID- LEVEL SIGNAL IS GOOD HOWEVER THE LOW LEVEL
FORCING IS NOT AS SUPPORTIVE. A STRONGER 850MB JET IS FOCUSED
WELL TO THE NORTH MONDAY NIGHT AND THE 850MB JET TUESDAY IS
STRONGER ACROSS MISSOURI. ULTIMATELY SOME OF THESE DETAILS WILL
CHANGE AS WE GET CLOSER AND TUESDAY INTO TUESDAY NIGHT IS THE BEST
CHANCE FOR RAIN DURING THE WEEK. THE RAIN MAY LINGER WEDNESDAY
DEPENDING ON THE PUSH OF THE FRONT. THURSDAY IS DRY. THE
TEMPERATURES HEAT UP WITH ISOLATED RAIN CHANCES FRIDAY AND
SATURDAY AND ISOLATED TO SCATTERED SUNDAY DEPENDING ON THE WHERE
THE FRONT IS.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1241 PM CDT SUN JUL 12 2020
VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD, WITH AFTERNOON
CUMULUS AND LIGHT NORTHERLY WINDS. COULD SEE A FEW SHOWERS
AROUND THIS AFTERNOON, MAINLY EAST OF THE MISSISSIPPI RIVER,
THOUGH EXPECT THOSE TO BE FEW AND FAR BETWEEN IF THEY DEVELOP.
WINDS SWITCH TO SOUTHERLY TONIGHT AND WILL PICK UP A BIT LATER
MONDAY MORNING. SOME HINTS AT SOME FOG IN THE AREA TONIGHT, BUT
LATEST GUIDANCE SUGGESTS WINDS ALOFT COULD BE JUST STRONG ENOUGH
TO PRECLUDE WIDESPREAD DEVELOPMENT, SO DID NOT INCLUDE IN THIS
ISSUANCE.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
SHORT TERM...CA
LONG TERM...ZAPOTOCNY
AVIATION...CA
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