AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
334 PM EDT WED APR 20 2005
.SHORT TERM...
IT WOULD SEEM SNOW IS IN OUR FORECAST. FIRST I WANT TO POINT OUT
GRR HAD 5.5 INCHES OF SNOW ON MAY 9TH 1923. SO YES...I REALLY CAN
HAPPEN THIS TIME OF YEAR IN GRR. SECOND THE ENSEMBLES OF THE GFS
LIKE THE IDEA AS DO THE ECMWF FOR SEVERAL RUNS AND SO DOES THE
CANADIAN AND UKMET. THE NAM IS ON BOARD WITH THE IDEA OF SNOW OVER
MOST OF SOUTHWEST MICHIGAN FRIDAY NIGHT INTO SATURDAY. THIRD POINT
ON THE SNOW ISSUE FOR LATE FRIDAY NIGHT AND SATURDAY IS THAT THE NAM
IS COLD ENOUGH AT ALL LEVELS FOR THIS EVENT. TYPICALLY THE NAM IS TO
WARM WITH THIS SORT OF THING AT THAT RANGE. USUALLY THE GFS IS TO
WARM. IF THEY MEET IN THE MIDDLE...IT'S STILL COLD ENOUGH FOR SNOW
ACROSS MOST OF OUR 23 COUNTY WARNING AREA SATURDAY DURING THE DAY.
WOULD YOU LIKE TO GUESS WHAT THE ISSUE WITH THIS FORECAST CYCLE IS?
TONIGHT...FRONT IS WELL SOUTH OF MICHIGAN AT 18Z AND HEADING AWAY.
MEANWHILE A 1026MB HIGH OVER ONTARIO IS HEADED OUR WAY. AS THE
SURFACE WINDS BECOME ANTICYCLONIC SKIES WILL CLEAR FROM NORTH TO
SOUTH. THE TREND IS SEEN NICELY ON THE VISIBLE SATELLITE IMAGES AS
THE CLEAR SKIES OVER CENTRAL ONTARIO PRECEDED SOUTH INTO NORTHERN
LOWER MICHIGAN AT 19Z. AS FOR THE TEMPERATURES TONIGHT...SINCE THE
POLAR JET IS STILL NORTH OF LOWER MICHIGAN BY 12Z THURSDAY AND HIGH
IS NEARLY OVERHEAD BY THEN SKIES SHOULD BE CLEAR AND SURFACE WINDS
LIGHT. I EXPECT TEMPERATURE TO BE NEAR OR BELOW FREEZING IN MOST
LOCATIONS NORTH AND EAST OF GRR.
THURSDAY HIGH PRESSURE RULES! THAT IS THANKS TO A SHORTWAVE RIDGE
MOVING OVER THE AREA IN RESPONSES TO BOTH THE SOUTHERN STREAM WAVE
SHEARING OUT OF THE WESTERN CLOSED UPPER LOW AND AN AMBITIOUS
NORTHERN STREAM SHORTWAVE HEADING SOUTH AFTER CRESTING THE REX BLOCK
UPPER LEVEL HIGH OVER WEST CENTRAL CANADA. SO WITH DEEP NORTHEAST
WINDS BECOMING EAST... A LOT OF DRY CANADIAN AIR MOVES IN. FEW CU
WILL BE FOUND OVER SOUTHWEST MICHIGAN THURSDAY AFTERNOON. SO MOSTLY
SUNNY OR JUST PLAIN SUNNY. TEMPERATURES WILL BE WARMER THAN MOS DUE
TO IT BEING MID APRIL (SUN ANGLE) AND NORTHEAST TO EAST WIND IS
MOSTLY DOWN SLOPE OVER OUR CWA. WHERE IT IS UPSLOPE THE AIR IS OFF
LAKE HURON AND THAT'S STILL COLD! EVEN SO... IT HAS A LONG WAY TO GO
BEFORE REACHING OUR CWA FROM THERE... SO HIGHS MOSTLY IN THE 50S
NORTH AND EAST TO THE LOWER TO MID 60S SOUTH AND WEST.
FRIDAY THE PHASING THING STARTS. A +90KT NORTHERN STREAM JET
SHARPLY DIGS THE NORTHERN STREAM JET SOUTH INTO MN AND THE EASTERN
DAKOTAS IN THAT TIME FRAME. AT THE SAME TIME SOME OF THE ENERGY FROM
THE SOUTHWEST UPPER LOW THAT SHEARED OUT TOWARD THE CENTRAL PLAINS
INDUCES A WAVE OUT ON THE POLAR FRONT WHICH BY FRIDAY MORNING WILL
BE A WELL DEVELOPED SURFACE LOW SOUTHWEST OF CHI. THIS WILL BRING
SHOWERS OR JUST PLAIN RAIN TO OUR CWA BY AFTERNOON. NOTE THE STRONG
ISENTROPIC ASSENT OVER SOUTHWEST MICHIGAN BY 12Z FRIDAY AND THE NEAR
0MB CONDENSATION PRESSURE DEFICITS. BOTTOM LINE...RAIN!
BY FRIDAY NIGHT THE COLD AIR FROM THE NORTHERN STREAM WAVE STARTS
PHASING WITH THE SOUTHERN STREAM SYSTEM. THICKNESS PLUNGE AND RAIN
CHANGES TO SNOW. ON SATURDAY THE SYSTEM DEEPENS TO OUR EAST AND
SOUTHWEST MICHIGAN IS ON THE WEST SIDE OF AN IMPRESSIVE CLOSED UPPER
LOW. ALL THE MODELS ARE COLD ENOUGH FOR SNOW AT ALL LEVELS... EVEN
THE NAM 1000/925MB THICKNESS IS COLD ENOUGH DURING THE DAY FOR SNOW
OVER MOST OF THE GRR CWA. IF THIS REALLY HAPPENS WE COULD BE LOOKING
AT 3 TO 6 INCHES BY SATURDAY EVENING. FOR NOW WILL GO WITH LIKELY
POP AND A MIX OF RAIN AND SNOW. IF LATER MODELS ARE SIMILAR... WE
MAY HAVE TO PUSH AN ALL SNOW EVENT FOR LATE FRIDAY NIGHT AND
SATURDAY IN OUR FORECAST.
.LONG TERM...
WILL MAKE SIGNIFICANT CHANGES TO THE EXTENDED PERIODS AS THE UPPER
LOW OVER THE EASTERN GREAT LAKES SHOULD EXIT VERY SLOWLY. THIS WILL
RESULT IN TEMPS REMAINING ON THE COOL SIDE AND ALSO A MORE PROLONGED
PERIOD OF SCATTERED RAIN AND SNOW SHOWERS. THE UPPER LOW IS
EXPECTED TO BE OVER SE OH BY SUNDAY MORNING...SLOWLY DRIFTING TO NW
PA MONDAY...AND FINALLY INTO SOUTHERN QUEBEC BY TUESDAY. CHILLY
CYCLONIC FLOW WILL HOLD TEMPS BELOW NORMAL AS WELL AS SUPPLYING
ABUNDANT LOW LEVEL MOISTURE. EXPECT SCTD PCPN WILL OCCUR SATURDAY
NIGHT THROUGH MONDAY ACROSS MUCH OF THE CWA. 1000-850 THICKNESS
VALUES CONTINUE TO SUPPORT SOME SNOW...ALTHOUGH IT REALLY DOES NOT
LOOK LIKE MUCH IN THE WAY OF ACCUMS ONCE WE GET PAST SATURDAY
NIGHT. THE SHOWERS SHOULD SLOWLY COME TO AN END FROM SW TO NE
MONDAY NIGHT AND INTO TUESDAY AS THE SYSTEM DRAGS THE LOW LEVEL
MOISTURE AWAY. WILL GO WITH A DRY TUESDAY NIGHT AND WEDNESDAY
DESPITE SOME UPPER TROFINESS THAT STILL LINGERS.
AS FOR TEMPS...MINS WILL MAINLY STAY IN THE 30S THROUGHOUT THE
EXTENDED. MAX TEMPS WILL REMAIN VERY CHILLY SUNDAY WITH THE CLOUDS
AND SHOWERS AROUND. WILL HAVE HIGH TEMPS FROM 40 TO 45. AS THE
SHOWERS BECOME LESS NUMEROUS TEMPS SHOULD RECOVER INTO THE 50 TO 55
DEGREE RANGE MONDAY...AND IN THE MID TO UPPER 50S TUESDAY AND
WEDNESDAY.
I guess it's justified for them to be so excited since it's been such a warm April - here we go towards the opposite end of normals. I just hope a major freeze doesn't end up killing the vegetation that is a good month ahead of schedule up here.
