Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 011656
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1256 PM EDT SAT AUG 1 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 251 AM EDT SAT AUG 1 2015

STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE SUNDAY AS A COLD FRONT
APPROACHES LOWER MICHIGAN. STRONG WINDS...HAIL...AND LOCALLY HEAVY
RAINFALL ARE THE MAIN THREATS. COOLER AND DRIER WEATHER MOVES INTO
THE REGION FOR THE MIDDLE PORTION OF NEXT WEEK.

&&

.UPDATE...
ISSUED AT 1053 AM EDT SAT AUG 1 2015

WE HAVE MADE SOME MINOR ADJUSTMENTS TO THE FCST FOR TODAY...
INCLUDING PULLING THE CHC OF SHOWERS ACROSS THE EAST TODAY AND
WARMING TEMPS UP A CATEGORY.

A LITTLE BIT OF MID LEVEL ACCAS TYPE CLOUD COVER IS DOTTING THE
AREA THIS MORNING AS A SHORT WAVE IS MOVING THROUGH NRN LOWER. THE
LOWER LEVELS BEING RELATIVELY STABLE AND DRY WITH DEW POINTS IN
THE 50S ARE LIMITING CLOUDS/PCPN BELOW 8K FT. THE SHORT WAVE WILL
ONLY BE MOVING EAST AWAY FROM THE AREA FROM NOW INTO THIS
AFTERNOON. SUBSIDENCE SETTLING IN BEHIND THIS WAVE AND A
STABILIZING FLOW OFF OF LAKE MICHIGAN SHOULD KEEP THE AREA DRY
THIS AFTERNOON.

WITH A GOOD DEAL OF SUNSHINE AND MIXING...H850 TEMPS OF 14 TO 15C
SHOULD YIELD TEMPS IN THE MID 80S AWAY FROM LAKE MICHIGAN. THIS
ALSO IS SUPPORTED BY THE MAX TEMPS YESTERDAY AND TREND EXPECTED
COMPARED TO TODAY.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 251 AM EDT SAT AUG 1 2015

THE THREAT FOR SEVERE WEATHER IS INCREASING FOR SUNDAY. THE ECMWF IS
BEING CLOSELY FOLLOWED DUE TO CONVECTIVE FEEDBACK PROBLEMS WITH
THE GFS AS EARLY AS FORECAST HOUR 24 IN IOWA (EVIDENT BY THE H250
WIND FIELDS AND H500 VORT/WINDS). DEEP LAYER SHEAR IS LOOKING
BETTER WITH THE 00Z MODEL RUNS...NOW APPROACHING 40 KNOTS BY 00Z
MON. THIS IS PARTLY DUE TO A MORE ROBUST LLJ APPEARING BETWEEN
18Z SUN AND 00Z MON...AT 45-50 KNOTS. SPC SREF MU CAPE IS SHOWING
2000-3000 J/KG SUNDAY AFTERNOON WITH BROOKS/CRAVEN SIG SEVERE
40000-50000. ALSO OF NOTE...THE ECMWF IS MORE AGGRESSIVE THAN THE
OTHER MODELS WITH 0-1KM HELICITY. IT IS SHOWING 200-250 M2/S2 FOR
00Z MON.

THE KEY WILL BE HOW MUCH INSTABILITY MOUNTS IN THE AFTERNOON IN
LIGHT OF POSSIBLE MORNING SHOWER OR STORM ACTIVITY. BASED ON HI-
RES MODEL SIM Z FROM THE NCEP WRF-ARW AND NCAR ENSEMBLES...SOME
SHOWERS AND STORMS ARE POSSIBLE IN THE MORNING AND MAYBE ANOTHER
BATCH MIDDAY. THIS DOES RAISE QUESTIONS ABOUT THE DEGREE OF
DESTABILIZATION THAT WILL OCCUR IN THE AFTERNOON...BUT THE WRF-
ARW AND ECMWF ARE SHOWING HEALTHY CONVECTIVE DEVELOPMENT SUNDAY
NIGHT ALONG THE FRONT...SO THE ATMOSPHERE MAY RECOVER. IF THIS
OCCURS...A LINE OF STRONG TO SEVERE THUNDERSTORMS MAY DEVELOP
ALONG THE COLD FRONT SUNDAY EVENING...PRODUCING SOME DAMAGING WIND
GUSTS AND LARGE HAIL.

POCKETS OF HEAVIER RAINFALL ARE POSSIBLE WITH ANY STORMS THAT
DEVELOP SUNDAY (MAYBE > 1"?)...THOUGH WITH DRY CONDITIONS OVER
THE LAST COUPLE WEEKS FOR MUCH OF THE REGION...THIS RAIN WILL BE
WELCOME NEWS FOR MANY. LOCALIZED PONDING OF WATER ON ROADS AND
SOME RISES IN SMALLER STREAMS AND CREEKS WOULD BE THE MAIN
IMPACTS.

FOR TODAY...A FEW SCATTERED SHOWERS MAY POP UP FOR CENTRAL AND
SOUTH CENTRAL LOWER MI. HI RES MODELS ARE INDICATING THIS
THREAT...AND SINCE A FEW DID DEVELOP YESTERDAY...THOUGHT IT WAS
WISE TO INCLUDE A LOW CHANCE THREAT FOR THIS AREA. STILL LOOKS TO
BE ON THE BREEZY SIDE TODAY THOUGH A FEW NOTCHES LOWER THAN
YESTERDAY.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 251 AM EDT SAT AUG 1 2015

A COOLER AND DRIER AIRMASS WILL MOVE IN THROUGH THE LONG RANGE
FORECAST PERIOD WITH PERSISTENT NW FLOW ALOFT AND AN UPPER LEVEL
TROUGH OVER THE GREAT LAKES AND EASTERN CONUS REGIONS. MAX TEMPS
TUESDAY THROUGH FRIDAY WILL ONLY REACH THE 70S WITH MINS MAINLY IN
THE 50S.

CANNOT COMPLETELY RULE OUT AN ISOLATED DIURNALLY DRIVEN SHOWER MID
TO LATE WEEK BUT DRY WX SHOULD PREVAIL THE VAST MAJORITY OF THE TIME
WITH A DRY AIRMASS IN PLACE AND AS A SFC HIGH PRESSURE RIDGE BUILDS
IN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1251 PM EDT SAT AUG 1 2015

GUSTY WINDS AT THE START AND THE END OF THE FORECAST PERIOD.
OTHERWISE...SCATTERED THUNDERSTORMS TO DEVELOP AFTER 10Z THAT MAY
IMPACT KMKG FOR A BRIEF TIME THOUGH AT THIS TIME AM ONLY CONFIDENT
ENOUGH TO INCLUDE A VICINITY MENTION. EXPECT GUSTY WINDS OVER
35KTS AND POTENTIALLY IFR VISIBILITIES AND CEILINGS IN AND NEAR
ANY THUNDERSTORMS.

REMAINDER OF THE AREA SHOULD SEE SCATTERED THUNDERSTORMS AT TIMES
ON SUNDAY BUT AT THIS TIME IT APPEARS THAT THE GREATEST CHANCE
LIES AFTER 18Z SUNDAY AND WILL NOT INCLUDE MENTION AT THIS TIME.

&&

.MARINE...
ISSUED AT 1053 AM EDT SAT AUG 1 2015

BASED ON STATE PARK OBSERVATIONS AND THE OFFSHORE BUOYS...WE HAVE
UPPED THE WAVES A BIT INTO THE 1-3 TO 2-4 FOOT CATEGORIES. WE DO
NOT EXPECT CONDITIONS TO GET HIGHER THAN THAT SO NO SMALL CRAFT
ADVISORIES OR BEACH HAZARDS STATEMENTS ARE ANTICIPATED FOR TODAY.

IT LOOKS LIKE WE MAY HAVE TO ISSUE SOME HEADLINES FOR BEGINNING AS
EARLY AS LATER TONIGHT AND MORE SO FOR SUN AS WINDS RAMP UP AHEAD
OF THE INCOMING SYSTEM.


&&

.HYDROLOGY...
ISSUED AT 309 PM EDT FRI JUL 31 2015

MOST BUT NOT ALL RIVER GAUGE SITES HAVE RETURNED TO NEAR NORMAL
STREAMFLOWS. MAIN CONCERN FOR PRECIPITATION OVER THE NEXT WEEK IS
SUNDAY. BASIN AVERAGE QPF OF HALF TO THREE-QUARTERS OF AN INCH
SHOULD NOT BE ENOUGH TO CAUSE A PROBLEM ON THE LARGER RIVERS.
HOWEVER... ANY THUNDERSTORMS THAT PERSIST COULD PRODUCE LOCALLY
HEAVY RAINFALL WHICH WOULD LEAD TO PONDING OF WATER AND MINOR
IMPACTS ON SMALLER RIVERS AND STREAMS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

UPDATE...NJJ
SYNOPSIS...HOVING
SHORT TERM...HOVING
LONG TERM...LAURENS
AVIATION...MACZKO
HYDROLOGY...CAS
MARINE...NJJ



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