FXUS63 KGRR 260318
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
837 PM EST FRI DEC 25 2009
LATEST UPDATE...MARINE...
.SYNOPSIS...(415 PM EST FRI DEC 25 2009)
LINGERING LIGHT RAIN SHOWERS LATE THIS AFTERNOON WILL GRADUALLY
CHANGE OVER TO SNOW SHOWERS FROM SOUTHWEST TO NORTHEAST THIS EVENING
AS COLDER AIR MOVES IN. INTERMITTENT SNOW SHOWERS ARE ANTICIPATED
THIS WEEKEND INTO MONDAY. DRY WEATHER WILL RETURN TUESDAY AS HIGH
PRESSURE BUILDS IN.
&&
.SHORT TERM...(415 PM EST FRI DEC 25 2009)
(TONIGHT THROUGH SATURDAY NIGHT)
PRIMARY SHORT TERM FCST CONCERNS INVOLVE DETERMINING PROBABILITIES
FOR SNOW SHOWERS FROM LATE THIS EVENING THROUGH SATURDAY NIGHT AS
WELL AS ASSESSING POTENTIAL FOR ACCUMULATIONS. FCST TWEAKS INCLUDED
RAISING POPS TO LIKELY SATURDAY THROUGH SATURDAY NIGHT FOR SEVERAL
LAKESHORE COUNTIES INCLUDING MASON AND OCEANA AND RAISING FCST SNOW
ACCUMS IN THAT TIME FRAME FROM WHITEHALL NORTH TO LDM.
KGRR/RGNL RADAR TRENDS SHOW RAIN SHOWERS WILL LINGER LATE THIS
AFTERNOON INTO THIS EVENING. LOW LEVEL CRITICAL THICKNESS TOOLS
SUGGEST SHOWERS WILL GRADUALLY CHANGE OVER TO SNOW SHOWERS THIS
EVENING FROM SSW TO NNE. SNOW ACCUMULATIONS OVERNIGHT SHOULD BE
LESS THAN AN INCH ACROSS MOST OF OUR CWFA.
HOWEVER SOME LOCALLY HIGHER AMOUNTS NEAR AN INCH TO INCH AND A HALF
ARE POSSIBLE RIGHT ALONG THE LAKE MI SHORELINE. THIS WILL BE DUE TO
SOUTHERLY FLOW LAKE EFFECT SNOW DEVELOPMENT AS H8 TEMPS FALL TO
AROUND -12 TO -13 C BY 12Z SAT.
THE OCCLUDED LOW PRESSURE SYSTEM WILL CONTINUE TO DRIFT ENE INTO OUR
AREA LATE TOMORROW AND TOMORROW NIGHT BRINGING LIGHT SNOW. WE
ANTICIPATE LIGHT ACCUMULATIONS OF ONLY AROUND AN INCH TO INCH AND A
HALF ACROSS THE MAJORITY OF OUR CWFA FROM SATURDAY THROUGH SATURDAY
NIGHT.
HOWEVER... SOUTHERLY FLOW LES AND LAKE ENHANCED SYNOPTIC SNOW MAY
CLIP PORTIONS OF OUR WESTERN LAKESHORE COUNTIES. THE BEST CHANCE FOR
THAT WOULD BE FROM NEAR WHITEHALL NORTH TO LUDINGTON... AND
ESPECIALLY AT BIG AND LITTLE SABLE POINTS. IN FACT I BELIEVE A SOLID
2 TO 4 INCH TYPE SNOWFALL (AT MINIMUM) IS CERTAINLY PLAUSIBLE AT THE
POINTS AND PERHAPS LDM AND PENTWATER FROM SATURDAY MORNING THROUGH
SATURDAY NIGHT... WITH LOCALLY HIGHER AMOUNTS CERTAINLY POSSIBLE.
THIS NOTION IS ALSO SUPPORTED BY 12Z GFS BUFKIT SNOWFALL PROGS FOR
LDM. THE BEST CHC FOR SNOW MAY COME TOWARD DAYBREAK SUNDAY AS LOW
LEVEL FLOW VEERS TO THE SSW RATHER THAN SSE TO SOUTH. WE ALSO
NOTICED THAT FCST SOUNDINGS SHOW INVERSION HEIGHTS UP TO AROUND 7 TO
10 KFT AGL IN LDM SATURDAY THROUGH SATURDAY NIGHT WITH DEEP MOISTURE
THROUGH THE DGZ.
&&
.LONG TERM...(415 PM EST FRI DEC 25 2009)
(SUNDAY THROUGH FRIDAY)
LONG TERM PERIOD BEGINS...WITH THE UPPER LOW THAT IS PRESENTLY
PIVOTING WESTWARD ACROSS IOWA...MOVING EAST ACROSS LAKE MICHIGAN ON
SUNDAY. THERE WILL BE SOME SYSTEM RELATED SNOW MOVING THROUGH THE
FORECAST AREA SUNDAY...BUT THERE WILL ALSO LIKELY BE SOME LAKE
ENHANCED SNOW IN WESTERLY FLOW. POTENTIALLY SOME DECENT SNOW BANDS
BETWEEN MUSKEGON...GRAND RAPIDS AND SOUTH HAVEN. SOME LIGHT LAKE
EFFECT SNOWS WILL CONTINUE IN NORTHWEST FLOW SUNDAY NIGHT AND MONDAY.
FAIRLY QUIET WEATHER IS EXPECTED MONDAY NIGHT THROUGH TUESDAY NIGHT
AS A RIDGE OF HIGH PRESSURE MOVES THROUGH THE GREAT LAKES REGION.
NEXT WEATHER MAKER SLIDES THROUGH THE AREA WEDNESDAY AND WEDNESDAY
NIGHT IN ZONAL FLOW. HAVE SNOW IN THE FORECAST BOTH PERIODS.
AN UPPER TROUGH SETTLES INTO THE AREA TOWARD THE END OF THE WEEK
WITH 850MB TEMPS COOLING DOWN. HAVE CHANCE POPS FOR LAKE EFFECT SNOW
SHOWERS THURSDAY AND FRIDAY.
$$
.AVIATION...(710 PM EST FRI DEC 25 2009)
THE SFC COLD FRONT/OCCLUSION IS CURRENTLY PUSHING IN FROM THE
SOUTH... WITH A BAND OF RAIN CONTAINING NUMEROUS IFR CEILINGS
PRECEDING IT. THIS BAND OF RAIN SHOULD PIVOT NORTH THROUGH THE TAF
SITES BY 02Z.
IT WILL BE COLD ENOUGH TO SUPPORT SNOW AFTER 02Z... ALTHOUGH THE
ARRIVAL OF A MID LEVEL DRY SLOT SHOULD KEEP THE SNOW PREDOMINATELY
ON THE LIGHT SIDE (4-6SM VSBYS) WITH CIGS ALSO MAINLY IN THE MVFR
CATEGORY.
DEEPER MOISTURE AND THE NEXT MID LEVEL SHORTWAVE PIVOTING AROUND THE
UPPER LOW IS EXPECTED TO ARRIVE FROM THE SOUTHWEST TOWARD 12Z. SNOW
SHOWER COVERAGE/INTENSITIES OUGHT TO INCREASE AS THIS OCCURS...
PARTICULARLY OVER THE WRN PORTION OF THE AREA. WILL GO WITH IFR SNOW
SHOWERS (2SM) AT MKG/GRR/AZO/BTL... AND MVFR (4SM) AT LAN/JXN.
THE PASSAGE OF THE SFC FRONT THIS EVENING WILL RESULT IN WINDS
SHIFTING FROM BEING OUT OF THE SOUTHEAST TO BEING OUT OF THE
SOUTH/SOUTHWEST. WIND SPEEDS FOR THE MOST PART WILL CONTINUE TO
AVERAGE AT OR ABV 12KTS UNTIL AFTER 18Z SAT WHEN THE SFC LOW DRAWS
CLOSER.
&&
.MARINE...(837 PM EST FRI DEC 25 2009)
SMALL CRAFT ADVISORY IN EFFECT THROUGH LATE SATURDAY NIGHT AS THE
WINDS HAVE FALLEN BELOW GALE FORCE. WAVES AND WINDS HAZARDOUS TO
SMALL CRAFT WILL CONTINUE INTO SATURDAY NIGHT AS A LOW PRESSURE
SYSTEM REMAINS IN THE REGION.
&&
.HYDROLOGY...(415 PM EST FRI DEC 25 2009)
NOT ENOUGH QPF FROM THIS SYSTEM TO CAUSE HYDRO ISSUES. IN
ADDITION... COLDER TEMPERATURES MAINLY IN THE 20S TONIGHT THROUGH
THE WEEKEND WILL RESULT IN FAIRLY MINOR FLUCTUATIONS IN AREA RIVER
LEVELS. LIGHT PCPN THROUGH THE WEEKEND AND MONDAY FOR MOST OF OUR
HSA WILL NOT RESULT IN ANY HYDRO ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY THROUGH 6Z SATURDAY NIGHT FOR THE ENTIRE
NEAR SHORE.
&&
$$
SYNOPSIS: LAURENS
SHORT TERM: LAURENS
LONG TERM: DUKE
AVIATION: MEADE
MARINE: 63
HYDROLOGY: LAURENS
