FXUS63 KGRR 240811
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
310 AM EST THU DEC 24 2009
LATEST UPDATE...ALL BUT AVIATION...
.SYNOPSIS...(310 AM EST THU DEC 24 2009)
A DEEP LOW OVER THE PLAINS WILL DRAW ABUNDANT MOISTURE NORTH FROM
THE GULF OF MEXICO. RAIN WILL MOVE NORTH AND TURN TO FREEZING RAIN
AND SLEET AS IT ENCOUNTERS COLDER LOW LEVEL TEMPERATURES. ICY
CONDITIONS CAN BE EXPECTED ACROSS THE REGION TONIGHT INTO CHRISTMAS.
WARMER AIR WILL MOVE NORTH CHRISTMAS MORNING TURNING THE
PRECIPITATION OVER THE RAIN. HOWEVER NORTH OF M-46...THE FREEZING
RAIN MAY LINGER INTO THE AFTERNOON. COLDER AIR WILL THEN WRAP INTO
LOWER MICHIGAN FROM THE SOUTH CHRISTMAS AFTERNOON. LIGHT RAIN WILL
TURN TO SCATTERED SNOW SHOWERS. THE COLDER AIR WILL LINGER THROUGH
THE WEEKEND AND SCATTERED TO NUMEROUS SNOW SHOWERS ARE EXPECTED.
&&
.SHORT TERM...(310 AM EST THU DEC 24 2009)
(TODAY THROUGH SATURDAY)
FORECAST CONCERNS DEAL WITH THE ICING POTENTIAL TODAY THROUGH
CHRISTMAS.
REGIONAL AND LOCAL RADAR SHOWS A LARGE BAND OF FREEZING
RAIN...SLEET...AND A LITTLE SNOW MOVING NORTH FROM ERN ILLINOIS
ACROSS LAKE MICHIGAN AND NORTH ACROSS THE WRN HALF OF THE LAKE SHORE
COUNTIES. THIS NWD PROGRESSION HAS BEEN VERY SLOW DUE TO THE VERY
DRY AIR ADVECTING EAST FROM CANADA. THIS HAS DELAYED THE ONSET OF
THE PCPN. THAT SAID...HOLLAND IS NOW REPORTING FZRA. THE CURRENT
WINTER WX ADVISORY ALONG THE LAKESHORE AND KAZO COUNTY RUNS THROUGH
14Z. GIVEN CURRENT RADAR TRENDS I CAN/T CANCEL IT. IT/S POSSIBLE
THAT PCPN WILL REMAIN ALONG THE WRN PORTION OF THE ADVISORY AREA
MUCH OF THE DAY. CERTAINLY THE FIM SUPPORTS THAT. THE NAM/SREF
DON/T. SO WE/LL RUN THE ADVISORY THROUGH 14Z. IT CAN BE EXTENDED IF
NEED BE.
THE NEXT HURDLE IS TONIGHT. CONFIDENCE IS HIGH THAT WE/LL SEE
FREEZING RAIN TONIGHT. SLEET IS A GOOD BET TOO. FORECAST SOUNDINGS
SHOW A PRONOUNCED WARM INTRUSION AROUND H8. PCPN WILL FORM AS RAIN
AND HIT THE GROUND AS FZRA/SLEET. TIMING IS IN QUESTION. THE GFS
BRINGS IN THE PCPN PRIOR TO 00Z. SO DOES THE FIM. BUT THE
NAM/ECMWF/SREF DON/T REALLY BRING IN PCPN UNTIL AFTER 06Z. GIVEN THE
UNCERTAINTY...WE ISSUED A WINTER WX ADVISORY BEGINNING AT 00Z. IT
RUNS THROUGH 22Z FRIDAY.
TEMPS ARE FCST TO WARM TOWARD 12Z FRIDAY. THIS SHOULD TURN THE FZRA
TO RAIN. THE DRY AIR ADVECTING IN FROM THE EAST MAY DELAY THE TURN
OVER HOWEVER. IT/S ALSO POSSIBLE THAT SECONDARY ROADS MAY REMAIN
SLICK FOR A WHILE LONGER. RATHER THAN ISSUE MULTIPLE ADVISORIES FOR
TONIGHT AND FRIDAY FOR BASICALLY THE SAME TYPE OF WEATHER AND
CONFUSE THINGS WE/LL RUN WITH ONE AND MENTION THE TIMING ISSUES IN
THE TEXT. WE CAN ALSO CANCEL COUNTIES FROM SOUTH TO NORTH FRIDAY AS
CONDITIONS PERMIT.
THIS IS AN OCCLUDED SYSTEM SO COLDER AIR WILL WRAP IN AROUND IT AND
WE/LL SEE IT DEVELOP FROM SOUTH TO NORTH. ACROSS THE SRN CWA FRIDAY
AFTERNOON THE RAIN WILL CHANGE BACK TO SHSN. OVER THE NORTH...WHERE
THE FZRA HAS THE HIGHEST CHANCE OF LINGERING THE LONGEST...THE FZRA
WILL TURN BACK TO SHSN AFTER 18Z. BY THAT TIME THE DRY SLOT WILL BE
WORKING IT/S WAY INTO THE CWA...SO ANY ACCUMS WILL BE KEPT TO A
MINIMUM.
WE EXPECT WINDS TO KICK UP...ESPECIALLY ALONG THE LAKE SHORE. 3HRLY
PRESSURE RISES IN THE 4-5MB RANGE ARE PROGD. THIS IS AN INCREASE
OVER YESTERDAY/S RUNS. ANY ICING WE GET WILL BE EXACERBATED BY THE
WIND. THIS MAY LEAD TO SPORADIC POWER OUTAGES.
SHSN WILL CONTINUE THROUGH SATURDAY AS THE UPPER LOW MOVES TOWARD
THE CWA AND COLD AIR REMAINS IN PLACE.
&&
.LONG TERM...(310 AM EST THU DEC 24 2009)
(SATURDAY NIGHT THROUGH WEDNESDAY)
OCCLUDED LOW MOVING THROUGH OVER THE WEEKEND WILL BRING SNOW SHOWERS
AND POSSIBLY SOME ACCUMULATIONS IN THE 2 TO 4 INCH RANGE WITH LAKE
ENHANCEMENT. WILL HAVE 50 POPS FOR SATURDAY NIGHT AND SUNDAY BUT
WILL PROBABLY NEED LIKELY ONCE THE TIMING IS PINNED DOWN A LITTLE
BETTER. LAKE EFFECT SNOW SHOWERS ON THE BACK SIDE OF THE UPPER LOW
PASSAGE BUT THESE WILL BE WINDING DOWN BY TUESDAY AS SFC RIDGING
BUILDS IN.
.AVIATION...(1155 PM EST WED DEC 23 2009)
THE MAIN AREA OF PRECIPITATION WAS STAYING WEST OF MI...BUT SOME
LIGHT MIXED PRECIPITATION WAS OBSERVED AROUND KBEH THIS EVENING.
KMKG IS THE MOST LIKELY TAF SITE TO SEE PRECIPITATION
OVERNIGHT...AND I WILL FEATURE SEVERAL HOURS OF MIXED SLEET AND SNOW
THROUGH 10Z. THERE IS A RISK THAT THE PRECIPITATION COULD LINGER
THROUGH 12Z DEPENDING ON HOW QUICKLY THE WAVE OF LOW PRESSURE
TRIGGERING IT MOVES THROUGH.
UNCERTAINTY EXISTS WITH REGARDS TO THE TIMING OF THE NEXT ROUND OF
PRECIPITATION THURSDAY OR THURSDAY NIGHT. THE MOST LIKELY SCENARIO
HAS FREEZING RAIN MOVING IN FROM THE SOUTH AFTER 22Z...WHICH IS WHAT
I WILL FEATURE WITH THE TAFS. THIS COULD EASILY BE DELAYED UNTIL
AFTER 06Z DEPENDING ON HOW THE UPSTREAM WAVE OF LOW PRESSURE EVOLVES.
ALL DATA INDICATES THAT BETWEEN 06Z AND 12Z ON THE 25TH THE BEST
SURGE OF PRECIPITATION ARRIVES. THERE WILL LIKELY BE A 6 TO 10 HR
BURST OF HEAVY PRECIPITATION. A MELTING LAYER IS EXPECTED TO BE
LOCATED ABOUT A MILE OFF THE GROUND. SURFACE TEMPERATURES WILL BE
CRITICAL...AS THEY WILL BE NEAR 32 DEGREES...WITH A COLDER LAYER
JUST ABOVE THE GROUND. SO AVIATORS SHOULD PLAN ON IMPACTS THEN DUE
TO THIS SCENARIO.
THIS FIRST BATCH OF PRECIPITATION IS EXPECTED TO WEAKEN EARLY
THURSDAY MORNING...BY 15Z. THEN WE WILL BE AWAITING THE
NEXT...STRONGER AREA OF FREEZING RAIN TO ARRIVE AFT 00Z FRI FROM THE
SOUTHWEST.
&&
.MARINE...(310 AM EST THU DEC 24 2009)
GALE WARNING REMAINS FOR ENE WINDS GUSTING TO 40 KNOTS THROUGH
CHRISTMAS DAY.
&&
.HYDROLOGY...(310 AM EST THU DEC 24 2009)
QPF POTENTIAL THURSDAY NIGHT AND FRIDAY WILL NOT BE HIGH ENOUGH TO
CAUSE HYDRO ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY EARLY THIS MORNING FOR THE LAKE
SHORE COUNTIES AND KALAMAZOO COUNTY.
WINTER WEATHER ADVISORY TONIGHT AND FRIDAY ENTIRE CWA.
LM...GALE WARNING FROM MIDDAY TODAY THROUGH FRIDAY AFTERNOON FOR
THE ENTIRE NEAR SHORE.
&&
$$
SYNOPSIS: 93
SHORT TERM: 93
LONG TERM: OSTUNO
AVIATION: MJS
MARINE: 93
HYDROLOGY: 93
