501
FXUS63 KIWX 192342
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
742 PM EDT MON APR 19 2021
SYNOPSIS
ISSUED AT 422 PM EDT MON APR 19 2021
RAIN CHANCES WILL SLOWLY DIMINISH WITH LOWS DROPPING INTO THE 30S.
RAIN WILL REDEVELOP TUESDAY ACROSS THE AREA, WITH A TRANSITION TO
ALL SNOW LATE AFTERNOON INTO TUESDAY EVENING. SNOWFALL TOTALS OF
2 TO 4 INCHES ARE POSSIBLE ALONG AND SOUTH OF US 24 AND EAST OF
INTERSTATE 69 WITH LESSER AMOUNTS NORTHWEST. THE WEDNESDAY MORNING
COMMUTE MAY BE SLICK, SO PLAN FOR EXTRA TIME TO REACH YOUR
DESTINATION. A FREEZE WARNING IS IN EFFECT FOR TUESDAY NIGHT AND
WEDNESDAY NIGHT, WITH LOW TEMPERATURES FALLING INTO THE 20S.
UPDATE
ISSUED AT 730 PM EDT MON APR 19 2021
CHANGES MADE TO SLOW DOWN SOUTHEAST PROGRESS OF RAINFALL AS BAND
CONTINUES TO REDEVELOP. QUESTIONS STILL REMAIN HOW FAR SOUTHEAST
THE RAIN WILL MAKE IT BEFORE SLOWLY DIMINISHING. HAVE BLENDED AS
BEST AS POSSIBLE TO KEEP SOME POPS OVERNIGHT BEFORE RAMP UP IN
POPS ON TUESDAY. OTHERWISE NO OTHER CHANGES.
SHORT TERM
(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 422 PM EDT MON APR 19 2021
BOTTOM LINE UP FRONT: UPGRADED TO A FREEZE WARNING FOR THE CWA GIVEN
HIGH CONFIDENCE IN TEMPERATURES TUESDAY NIGHT AND WEDNESDAY NIGHT
FALLING BELOW 32 DEGREES. EVEN IF WE DO GET CLOUD COVER, THE AIRMASS
IS COLD ENOUGH THAT WE'LL SEE AT LEAST UPPER 20S IN MOST AREAS, IF
NOT MID 20S. IT IS A LITTLE BIT EARLIER THAN WE USUALLY ISSUE
WARNINGS BUT GIVEN THE SIGNIFICANT IMPACTS UPPER 20S WILL HAVE ON
THE FRUIT CROPS AND OTHER VULNERABLE VEGETATION, FIGURED WE MIGHT AS
WELL ENSURE THE WORD IS OUT. CURRENT FORECAST HAS LOWS OF 23F TO
AROUND 30F, WITH LOCATIONS CLOSE TO LAKE MI CLOSER TO 32F.
AS FOR OUR POTENTIAL SNOW EVENT, THE UPPER LEVEL JET STILL LOOKS TO
PROVIDE THE BEST FORCING BETWEEN 00-6Z TUESDAY NIGHT, WITH THE MID
LEVEL TROUGH TO THE WEST OF OUR CWA PROVIDING A BROAD REGION OF DVA-
STRONGEST IN THE SOUTHEAST. INSTABILITY STILL LOOKS FAVORABLE IN
THAT AREA FOR HIGHER RATES, WITH NEGATIVE EPV ABOVE THE FRONTAL
ZONE.REGARDING ANY WINTER WEATHER ADVISORIES AND WARNINGS, STILL NOT
THE GREATEST CONFIDENCE IN SNOW TOTALS AND THE IMPACTS FOR SO WILL
HOLD OFF FOR NOW ON ISSUING ANYTHING. THE SOUTHEASTWARD SURFACE LOW
PRESSURE TRACK TREND CONTINUES, AND MODELS ARE COMING MORE IN LINE
WITH ONE ANOTHER IN REGARDS TO THE TIMING. HOWEVER, THEY DIFFER
QUITE A BIT AS FAR AS THE MAGNITUDE AND LOCATION OF THE HIGHEST QPF,
WITH THE NAM THE FARTHEST NORTHWEST DETERMINISTICALLY SPEAKING.
THERE IS ALSO STILL QUITE A BIT OF SPREAD IN ENSEMBLE DATA. THE
ECMWF, GEM, AND OF COURSE, THE GFS-HAVE ALL TRENDED SOUTHEAST. USED
AROUND A 10:1 RATIO, WITH MOSTLY A RAIN/SNOW MIX TUESDAY AFTERNOON
TRANSITIONING TO ALL SNOW FROM WEST TO EAST TUESDAY EVENING.
AS FAR AS ACCUMULATIONS GO, I HAVE AROUND 2 TO 4 INCHES SOUTH OF US
24 AND UP TO 2 INCHES NORTH OF US 24, WITH THE HIGHEST TOTALS EAST
OF I-69. THE TEMPERATURES TUESDAY AFTERNOON ARE A LITTLE HIGHER THAN
PREVIOUSLY FORECASTED IN ALIGNMENT WITH THE LATEST MODEL GUIDANCE,
BUT IT'S POSSIBLE THE TEMPS END UP BEING A LITTLE LOWER AFTER 18Z IN
THE NORTHWEST. IF THIS HAPPENS, WE'LL TRANSITION TO ALL SNOW A
LITTLE EARLIER THAN I CURRENTLY HAVE IN THE FORECAST (AFTER 00Z). I
DID LOWER THEM A LITTLE BIT FROM WHAT THE MODELS SUGGESTED TO
ACCOUNT FOR THE POTENTIALLY FASTER COOLING, BUT DIDN'T HAVE THE
CONFIDENCE TO LOWER MUCH MORE THAN MID-UPPER 30S. IF WE DO
TRANSITION EARLIER TUESDAY AFTERNOON WE COULD ADD UP TO ANOTHER INCH
OF SNOW TO THE FORECAST IN THE NORTHWEST (HENCE THE WORDING "UP TO
2").
ON WEDNESDAY, THE UPPER TROUGH (OR CLOSED LOW AT THIS POINT) DRIFTS
SLOWLY OVER LOWER MICHIGAN, TAKING THE BEST FORCING QUICKLY TO THE
EAST. HOWEVER, A SHORTWAVE PIVOTS AROUND THE BASE, WHICH WILL BRING
US CHANCES FOR SHOWERS IN THE SOUTH AND WESTERN FORECAST AREA IN THE
AFTERNOON. HAVE HIGHS REACHING UP TO ABOUT 40-48 DEGREES (WARMEST
SOUTHWEST), SO WE WILL HAVE CHANCES FOR RAIN/SNOW SHOWERS.
LONG TERM
(THURSDAY THROUGH MONDAY)
ISSUED AT 422 PM EDT MON APR 19 2021
TEMPS MODERATE FOR THE END OF THE WEEK THOUGH STILL SLIGHTLY ON THE
COOL SIDE OF NORMAL. CUT INITIAL BLENDED HIGHS OVER THE WEEKEND WITH
POTENTIAL FOR PRECIP SAT AND GENERAL NW FLOW. LATEST GUIDANCE
SUGGESTS FRIDAY WILL REMAIN DRY WITH NEXT HIGH AMPLITUDE TROUGH
ARRIVING ON SAT WITH NEXT CHANCE OF RAIN. 12Z GUIDANCE IN DECENT
AGREEMENT ON LONGWAVE RIDGE DEVELOPMENT EARLY NEXT WEEK YIELDING
MUCH WARMER TEMPS.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 730 PM EDT MON APR 19 2021
PERIOD OF FUEL ALTERNATE CONDITIONS (CIGS) AS ARRIVED AT KSBN, BUT
IT WILL LIKELY BE SHORT LIVED, ENDING AS THE RAIN SINKS SOUTH AWAY
FROM THE SITE. TAF TRENDS HAVE BEEN ADJUSTED TO REFLECT THIS WITH
TRANSITION BACK TO VFR AFTER 2Z. AT KFWA FORECAST MORE PROBLEMATIC
WITH EXPECTED DECREASE IN PRECIP WITH TIME. FUEL ALTERNATE
CONDITIONS MAY STAY AWAY FROM THE SITE, BUT MVFR CIGS WILL LIKELY
DOMINATE AS THE FRONT STALLS OUT.
FOCUS THEN SHIFTS TO RETURN OF RAIN BETWEEN 15 AND 19Z AT BOTH
SITES (KSBN FIRST). STILL CHALLENGES AS TO HOW FAST THE PRECIP
WILL SHIFT SOUTH AND COLD AIR ARRIVE TO CAUSE A SWITCH TO A MIX OF
RA/SN AS WELL EVENTUAL CHANGE TO ALL SNOW. HAVE LEFT ALL RAIN WITH
MVFR CIGS MOVING BACK IN AT BOTH LOCATIONS WITH THE ARRIVAL OF THE
RAIN, THEN POTENTIAL TRANSITION TO IFR CONDITIONS MAINLY AT KFWA
AS BOTH CIGS DROP AND TRANSITION TO SNOW OCCURS (THE TRANSITION
LIKELY MORE AFTER 00Z). EXPECTED FURTHER CHANGES TO BOTH TAFS AS
WE GET CLOSER TO THE EVENT.
IWX WATCHES/WARNINGS/ADVISORIES
IN...FREEZE WARNING FROM 10 PM EDT /9 PM CDT/ TUESDAY TO 8 AM EDT /7
AM CDT/ THURSDAY FOR INZ003>009-012>018-020-022>027-032>034.
MI...FREEZE WARNING FROM 10 PM TUESDAY TO 8 AM EDT THURSDAY FOR
MIZ077>081.
OH...FREEZE WARNING FROM 10 PM TUESDAY TO 8 AM EDT THURSDAY FOR
OHZ001-002-004-005-015-016-024-025.
LM...NONE.
UPDATE...FISHER
SYNOPSIS...MCD
SHORT TERM...MCD
LONG TERM...AGD
AVIATION...FISHER
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