000
FXUS63 KGRR 111512
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1112 AM EDT SAT MAY 11 2013

LATEST UPDATE...
UPDATE/MARINE

.SYNOPSIS...
ISSUED AT 334 AM EDT SAT MAY 11 2013

A COLD FRONT WILL MOVE THROUGH LOWER MICHIGAN TODAY BRINGING SHOWERS
WITH IT. COOLER WEATHER WILL FOLLOW FOR SUNDAY WITH WIDESPREAD FROST
EXPECTED SUNDAY NIGHT. A DRAMATIC WARM UP WILL DEVELOP EARLY NEXT
WEEK WITH HIGHS REACHING THE 80S MIDWEEK.

&&

.UPDATE...
ISSUED AT 1106 AM EDT SAT MAY 11 2013

NOTICED SOME LIGHTNING WITH THE CELL WEST OF LITTLE SABLE POINT.
BASED ON THIS I ADDED THUNDER TO THE FORECAST FOR SOUTHWEST MI
THIS AFTERNOON. THIS FRONT WILL MOVE QUICKLY THROUGH THE REGION
THIS AFTERNOON. BY 22Z IT SHOULD BE EAST OF LANSING. POPS WERE
ADJUSTED SLIGHTLY BECAUSE OF THE FASTER FRONTAL MOVEMENT.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 334 AM EDT SAT MAY 11 2013

FORECAST CONCERNS DEAL WITH PCPN TRENDS TODAY AND FROST/FREEZE
CHANCES TONIGHT AND SUNDAY NIGHT.

LOW PRESSURE OVER WISCONSIN WILL DRAG A COLD FRONT ACROSS THE CWA
THIS AFTERNOON. REGIONAL RADAR SHOWS A BROKEN LINE OF SHOWERS MOVING
ACROSS THE UPPER MIDWEST. LOOK FOR THIS TO FILL IN A BIT BETTER THIS
AFTERNOON. WE DON/T EXPECTED TO MUCH RAIN WITH THIS AS MOISTURE IS
SOMEWHAT LIMITED. CAN/T RULE OUT THUNDER AS MUCAPES ARE IN THE
150-200 J/KG RANGE BUT OVERALL INSTABILITY IS ON THE LOW SIDE.

COLDER AIR WILL FLOW INTO THE CWA TONIGHT AND FROST IS POSSIBLE OVER
THE NRN 2 TIERS OF COUNTIES. COLD ADVECTION WILL CONTINUE SUNDAY AS
H8 TEMPS FALL TO -8C WHICH WILL YIELD LAKE DELTA T/S AROUND 13C.
SHOULD SEE SOME LAKE CLOUDS WITH THIS SETUP ALONG WITH A CHANCE OF
SHOWERS...SOME OF WHICH MAY BE MIXED WITH SNOW OVER THE NRN CWA.

AS THE UPPER TROUGH MOVES AWAY SUNDAY NIGHT SKIES SHOULD CLEAR AND
TEMPS WILL FALL INTO THE 20S/LWR 30S. WIDESPREAD FROST IS EXPECTED
WITH FREEZING TEMPS OVER MUCH OF THE CWA. A FREEZE WARNING MAY BE
NEEDED SUNDAY NIGHT.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 334 AM EDT SAT MAY 11 2013

TYPICAL OF SPRING IN MICHIGAN OUR WARM THEN COLD THEN WARM AGAIN
WEATHER PATTERN WILL CONTINUE. MY ISSUE TODAY IS MOSTLY FOCUSED ON
WHAT HAPPENS TO THE FRONT THAT MOVES INTO THE AREA WEDNESDAY... DOES
IT STALL NEAR SOUTHWEST MICHIGAN PUTTING US BACK INTO A RAINY
PATTERN OR DOES IT SLIP FAR ENOUGH SOUTH TO DRY US OUT LATE THIS
COMING WEEK?

THE LARGE SCALE PATTERN CONTINUES TO FEATURE A HIGH AMPLITUDE UPPER
AIR PATTERN WITH CONSIDERABLE MERIDIONAL FLOW (WHY IT IS GETTING SO
COLD THIS WEEKEND). ALL OF THE OPERATIONAL MEDIUM RANGE MODELS
CONTINUE TO SUGGEST THIS PATTERN WILL FLATTEN OUT EARLY THIS COMING
WEEK. WE END UP WITH ONE OF THOSE EXTENDED EAST ASIAN JET FEATURES
BY MIDWEEK. TYPICALLY FOR SOUTHWEST MICHIGAN THAT MEANS WARMER THAN
NORMAL TEMPERATURES AND FREQUENT SHORTWAVES PRODUCING FREQUENT
PERIODS OF PRECIPITATION. ALL OF THIS HAS BEEN AND CONTINUES TO BE
THE MAIN ASPECT OF THE CHANGING UPPER AIR PATTERN. SO THE QUESTION
BECOMES... DOES THE FLATTER FLOW FORECAST BY THE ECMWF FROM
WEDNESDAY ON BECOME THE TRUE PATTERN OR WILL THE MORE AMPLIFIED
PATTERN OF THE GFS PREVAIL (THAT WOULD BE DRIER AND COOLER FOR
SOUTHWEST MICHIGAN)?

THERE ARE TWO CONCERNS OF MINE AS TOO WHY I QUESTION THE ECMWF THIS
TIME. FIRST IS THE SYSTEM MOVING ONTO THE WEST COAST CURRENTLY IS A
VERY DEEP TROUGH WITH A STRONG PACIFIC SYSTEM MOVING THROUGH THE
BASE OF THE TROUGH (JUST OFF THE OR/WA COAST). THE ECMWF FLATTENS
THIS WAVE AMAZINGLY FAST GIVEN ITS CURRENT AMPLITUDE.  ALSO BOTH THE
ECMWF AND GFS SHOW A CLOSE UPPER HIGH DEVELOPING BY TUESDAY JUST
SOUTH OF GREENLAND. THAT THEN PERSISTS ON BOTH MODELS THROUGH THE
REST OF THE WEEK. OUR UPPER AIR FLOW WILL BE BLOCKED TO OUR EAST.
GIVEN THE BLOCKING TO THE EAST AND STRENGTH OF THE PACIFIC SYSTEM
MOVING ON SHORE (OUR WEDNESDAY SYSTEM) I WOULD HAVE TO FAVOR THE GFS
AT THIS POINT(MORE AMPLIFIED UPPER AIR PATTERN).

THE MORE AMPLIFIED PATTERN WOULD SUPPORT A STRONG COLD FRONT
WEDNESDAY EVENING WITH STRONGER THUNDERSTORMS BUT IT WOULD ALSO MEAN
A WARMER WEDNESDAY... THICKNESS VALUES AND 850 AND 925 MB TEMPS ARE
FORECAST TO BE AS WARM ENOUGH FOR LOWER TO MID 80S WEDNESDAY. SO I
HAVE TO IMAGINE EVEN WITH SOME FRONTAL CLOUDS AROUND MOST INLAND
AREAS SHOULD SEE HIGHS INTO THE LOWER 80S WEDNESDAY. WITH THAT MORE
AMPLIFIED PATTERN THE FRONT WOULD GO SOUTH OF MICHIGAN THURSDAY AND
IT WOULD COOL OFF SOME FOR THE REST OF THE WEEK.

IF THE ECMWF IS CORRECT... THE UPPER LOW OVER THE SW CONUS GETS
BOOTED EAST NORTHEAST TOWARD THE GREAT LAKES AND THAT BRING US A
STALLED FRONT WITH PERIODS OF SHOWERS AND THUNDERSTORMS WEDNESDAY
THROUGH FRIDAY (AND BEYOND).

FOR NOW I WILL SLIGHTLY FAVOR THE GFS AND KEEP POPS LOW WED THROUGH
FRIDAY. WE SHALL SEE HOW THIS PLAYS OUT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 748 AM EDT SAT MAY 11 2013

IFR CIGS WILL LIFT TO MVFR WITH SHOWER BY MIDDAY THEN IMPROVE TO
SOLID VFR AND IT MAY EVEN CLEAR FOR A FEW HOURS LATE THIS
AFTERNOON. HOWEVER IT WILL BE WINDY FROM MID AFTERNOON INTO THE
EVENING BEHIND THE COLD FRONT.

AS THE PREVIOUS SHIFT EXPECTED THE LOW CLOUDS PERSISTED THROUGH
THE NIGHT INTO THE MID MORNING HOURS. CEILING DID COME DOWN FROM
MVFR TO IFR ACROSS THE TAF SITES. WITHIN THE LAST HOUR MKG WENT
DOWN TO LIFR WITH FOG.

I WOULD EXPECT THE MIXING AHEAD OF THE COLD FRONT IN CONJUNCTION
WITH DAY TIME HEATING... THE CEILING WILL AT LEAST IMPROVE TO MVFR
BY LATE MORNING. AT 1140Z THERE REMAINS A SOLID BAND OF SHOWERS
JUST AHEAD OF THE COLD FRONT OVER WISCONSIN. THEY WILL CROSS THE
GRR AREA BTW 16Z AND 19Z AND THE LAN AREA BETWEEN 19Z AND 22Z.
THERE IS MARGINALLY ENOUGH INSTABILITY FOR A FEW THUNDERSTORMS BUT
THEY SHOULD BE TO WIDELY SCATTERED TO PUT IN THE TAF FORECAST.

STRONG SUBSIDENCE BEHIND THE COLD FRONT WILL CLEAR SKIES LATE THIS
AFTERNOON AND INCREASE THE WIND SPEED TO 15 TO 25 MPH WITH HIGHER
GUSTS. WRAP AROUND MOISTURE WILL BRING LOW CLOUDS BACK AFTER
MIDNIGHT BUT I DID NOT PUT THEM IN THE CURRENT TAF EXCEPT FOR MKG
TO KEEP THE TAFS AS SIMPLE AS POSSIBLE.




&&

.MARINE...
ISSUED AT 1106 AM EDT SAT MAY 11 2013

STRONGER GUSTS TO GALE FORCE ASSOCIATED WITH THE COLD FRONT ARE
SHOWN ON THE HRRR RUC. FSL RUC HAD GUSTS OVER 30 KNOTS. STABILITY
OF THE LAKE MAY BE AN ISSUE...LIMITING THIS RISK. SO FAR THE HRRR
IS VERIFIY WELL WITH THE UPSTREAM GUSTS. WENT AHEAD AND ISSUED A
GALE WARNING. THE WINDS WILL BE SHIFTING SHARPLY...ADDING TO THE
HAZARD. BY 00Z A LULL IN THE WINDS IS FORECASTED...SO THE GALE
WARNING IS OF A SHORTER DURATION. MAY NEED TO EXTEND IT AS THE
WINDS WILL PICK BACK UP BY DAYBREAK SUNDAY.

&&

.FIRE WEATHER...
ISSUED AT 334 AM EDT SAT MAY 11 2013

SHOWERS ARE EXPECTED MAINLY THIS AFTERNOON. COOLER TEMPERATURES WILL
FOLLOW SUNDAY WITH HIGHS IN THE 40S.

&&

.HYDROLOGY...
ISSUED AT 334 AM EDT SAT MAY 11 2013

RAINFALL LESS THAN A QUARTER INCH TODAY WILL HAVE A NEGLIGIBLE
EFFECT ON RIVERS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...93
SHORT TERM...93
LONG TERM...WDM
AVIATION...WDM
FIRE WEATHER...93
HYDROLOGY...93
MARINE...MJS