FXUS63 KGRR 260936
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
435 AM EST SAT DEC 26 2009
LATEST UPDATE...ALL BUT AVIATION...
.SYNOPSIS...(435 AM EST SAT DEC 26 2009)
A SLOW MOVING LOW PRESSURE SYSTEM OVER ILLINOIS WILL KEEP THE
WEATHER COLD WITH SNOW SHOWERS HERE IN LOWER MICHIGAN THROUGH THE
WEEKEND. ACCUMULATIONS ARE POSSIBLE...ESPECIALLY NEAR THE
LAKESHORE. THIS SYSTEM WILL PULL AWAY SLOWLY EARLY NEXT WEEK WITH
TEMPERATURES EXPECTED TO BE CLOSE TO NORMAL.
&&
.SHORT TERM...(435 AM EST SAT DEC 26 2009)
(TONIGHT THROUGH MONDAY)
THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE SNOWFALL AMOUNTS
AND TRENDS THROUGH THE WEEKEND.
FIRST OFF..THE FREEZING RAIN HAS ENDED... BUT A LAYER OF ICE IS
UNDERNEATH THE SNOW. CONDITIONS ARE LIKELY TO REMAIN SLICK ON ANY
UNTREATED SURFACES THROUGH THIS MORNING. SOME OF THE SNOW WILL BE
LOCALLY HEAVY AS THE LOW LEVEL VORT MAX LIFTING NORTHWARD OUT OF
INDIANA PIVOTS THROUGH SOUTHWEST LOWER MI. CLOUD TOPS HAVE BEEN
COOLING WITH THIS FEATURE AND RECENTLY KGSH DROPPED TO 3/4SM.
MODELS DATA SUGGESTS THIS FEATURE WILL STRENGTHEN AS IT MIGRATES
THROUGH THE AREA. I WILL KEEP THE WINTER WEATHER ADVISORY GOING
THROUGH THE MORNING AS TRAVEL IMPACTS ARE LIKELY DUE TO THE ICY
SURFACES AND AREAS OF REDUCED VISIBILITIES.
RATHER INTERESTING SETUP FOR LATER THIS AFTERNOON INTO TONIGHT.
ANOTHER VORT LOBE PIVOTS IN FROM THE SOUTHWEST. THE MOISTURE
DEEPENS AS A THERMAL TROF AT 850 MB TO 700 MB ARRIVES. LOW LEVEL
CONVERGENCE IS FOCUSED MAINLY WEST OF HIGHWAY 131 FROM 00Z TO 06Z
FROM THE NAM. THIS RAISES THE RISK FOR SOME LOCALLY HEAVIER
SNOW...ESPECIALLY UP THE LAKESHORE NORTH OF HOLLAND. MAY NEED TO
COVER THE SITUATION WITH ADVISORIES AND THERE IS EVEN A LOW RISK FOR
A WARNING EVENT DEPENDING ON HOW THE SITUATION UNFOLDS.
ANOTHER LOW OF VORTICITY ARRIVES SUNDAY WITH THE ACTUAL COLD POOL
ALOFT. WILL FEATURE LIKELY POPS FOR MAINLY WESTERN COUNTIES AS
ACCUMULATING SNOW IS EXPECTED.
WHILE THE UPPER COLD POOL IS PULLING AWAY ON MONDAY...A REINFORCING
SHOT OF SHALLOW COLD AIR DROPS DOWN FROM THE NORTH. THIS FEATURE
WILL LIKELY KEEP THE SNOW SHOWERS GOING...ESPECIALLY NEAR THE
LAKESHORE.
&&
.LONG TERM...(435 AM EST SAT DEC 26 2009)
(MONDAY NIGHT THROUGH FRIDAY)
THE MID RANGE MODELS ARE IN DECENT AGREEMENT IN A SETUP WITH SLOW
MOVING SYNOPTIC SCALE FEATURES. TIMING OF A SYSTEM APPROACHING THE
REGION WEDNESDAY OR WEDNESDAY NIGHT IS THE MAIN ISSUE WITH THIS
FORECAST PACKAGE. ONLY SMALL CHANGES NEEDED AND/OR MADE TO THE GRIDS.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN AS HIGH PRESSURE
BUILDS INTO THE REGION BEHIND A SLOW MOVING LOW PRESSURE SYSTEM
MONDAY NIGHT. FAIRLY QUIET WEATHER IS THEN EXPECTED THROUGH TUESDAY
NIGHT... AS THE RIDGE OF HIGH PRESSURE MOVES THROUGH THE GREAT LAKES
REGION.
THE NEXT LOW WILL APPROACH THE REGION LATE WEDNESDAY OR WEDNESDAY
NIGHT. THE ECMWF MOVES THE LOW NORTH OF THE AREA WHILE THE GFS MOVES
IT SLOWLY OVER THE AREA AS AN UPPER LEVEL LOW MEANDERS ACROSS THE
REGION. WITH EITHER SOLUTION... SNOW AND UNSETTLED WEATHER WILL BE
POSSIBLE FOR OUR FORECAST AREA THROUGH FRIDAY. THE SNOW LOOKS TO BE
LIGHT IN THE LONG TERM PERIODS.
THE HIGH TEMPERATURES TUESDAY AND FRIDAY SHOULD BE A BIT BELOW
NORMAL AS COOLER AIR IS MOVING IN ON THESE DAYS AND TEMPERATURES FOR
THE REST OF THE LONG TERM SHOULD BE AROUND NORMAL. NORMAL LOWS ARE
IN THE UPPER TEENS WITH NORMAL HIGHS AROUND 30 DEGREES F.
$$
.AVIATION...(1215 AM EST SAT DEC 26 2009)
THE COLD AIR HAS BEEN POURING IN FROM THE SOUTH TONIGHT AND
PRECIPITATION HAS CHANGED OVER TO A MIXTURE OF FREEZING RAIN...
SLEET AND SNOW. THIS MIX WILL GO TO ALL SNOW VERY SOON WITH
CONTINUED COLD AIR ADVECTION... SO WILL NOT CARRY ANY FRZG RAIN IN
THE 06Z TAFS. GENERALLY MVFR CONDITIONS WILL PREVAIL THROUGH 12Z....
ALTHOUGH A FEW HOURS OF DRY SLOTTING APPROACHING FROM THE SOUTHWEST
INBETWEEN VORT LOBES MAY BRING A BRIEF PERIOD OF VFR CONDITIONS.
DEEPER MOISTURE AND THE NEXT MID LEVEL SHORTWAVE PIVOTING AROUND THE
UPPER LOW IS EXPECTED TO ARRIVE FROM THE SOUTHWEST TOWARD/AFTER 12Z.
SNOW SHOWER COVERAGE/INTENSITIES OUGHT TO INCREASE AS THIS OCCURS...
PARTICULARLY OVER THE WRN PORTION OF THE AREA AND ESPECIALLY IN THE
AFTERNOON. WILL GO WITH IFR SNOW SHOWERS (1-3SM) DEVELOPING AT
MKG/GRR/AZO/BTL... AND MVFR (4-5SM) AT LAN/JXN.
&&
.MARINE...(435 AM EST SAT DEC 26 2009)
WILL MAINTAIN THE SMALL CRAFT ADVISORIES AS GUSTY WINDS AND COLD AIR
ADVECTION WILL LIKELY KEEP CONDITIONS HAZARDOUS FOR SMALL CRAFT
THROUGH TODAY.
&&
.HYDROLOGY...(435 AM EST SAT DEC 26 2009)
TEMPERATURES ARE FALLING AND THAT WILL LIKELY LOCK UP ANY ADDITIONAL
RUNOFF FROM THE SNOW MELT AND RECENT RAINFALL. SO WHILE RISES ARE
EXPECTED ON AREA STREAMS AND RIVERS...THEY ARE EXPECTED TO BE
MINIMAL.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY ALL COUNTIES UNTIL 11 AM SAT.
LM...SMALL CRAFT ADVISORY THROUGH 6Z SATURDAY NIGHT FOR THE ENTIRE
NEAR SHORE.
&&
$$
SYNOPSIS: MJS
SHORT TERM: MJS
LONG TERM: 63
AVIATION: MEADE
MARINE: MJS
HYDROLOGY: MJS
