Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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083
FXUS63 KGRR 300730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT SAT JUL 30 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 308 AM EDT Sat Jul 30 2016

PERIODS OF SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TODAY
INTO SUNDAY. SOME OF THE SHOWERS WILL BE LOCALLY VERY HEAVY WITH
THE POTENTIAL FOR LOCALIZED FLOODING. IT WILL BE COOLER TOO WITH
HIGHS ONLY IN THE UPPER 70S TO LOWER 80S BOTH TODAY AND SUNDAY.
THE SLOW MOVING STORM THAT IS CAUSING ALL OF THIS RAINFALL WILL
FINALLY MOVE OUT OF THE AREA BY SUNDAY NIGHT. THIS WILL ALLOW
LARGE HIGH PRESSURE SYSTEM TO MOVE OVER MICHIGAN CLEARING THE
SKIES AND BRINGING WARMER AFTERNOON TEMPERATURES.

A WARM FRONT WILL COME THROUGH THE AREA ON WEDNESDAY PUTTING
SOUTHWEST MICHIGAN BACK INTO THE HOT AND HUMID AIR. A COLD FRONT
WILL MOVE INTO THE AREA THURSDAY WITH THE THREAT OF THUNDERSTORMS
BUT NOT BEFORE HIGHS REACH INTO THE 90S.


&&

.SHORT TERM...(Today through Monday)
Issued at 308 AM EDT Sat Jul 30 2016

THE MAIN ISSUE TODAY IS THE THREAT OF LOCALIZED FLOODING FROM SLOW
MOVING HEAVY RAIN SHOWERS (THUNDERSTORMS). THIS THREAT REALLY GOES
INTO SUNDAY AS THE SYSTEM CREATING ALL OF THIS WILL LIKELY NOT
MOVE OUT OF THE AREA UNTIL SUNDAY NIGHT.

WE HAVE PRECIPITABLE WATER VALUES NEAR 1.75 INCHES THIS AFTERNOON
OVER A GOOD PART OF OUR CWA. WHILE THAT IS HAPPENING WE HAVE THE
DEFORMATION AXIS IN THE 500 TO 700 MB LAYER FROM NEAR MBS TO GRR
AND NOT TO Surprizingly WE HAVE DECENT UPPER divergance OVER THIS
SAME AREA THIS AFTERNOON. ALL OF THIS IS CAUSED BY THE NEXT
UPSTREAM SHORTWAVE (CURRENTLY NEAR NEBRASKA AND Kansas) MOVING
INTO THE TROUGH OVER THE GREAT LAKES. THAT signficantly INCREASE
THE UPPER DIVERGENCE AND IN TURN LIFT. SO I SEE BANDS OF SHOWERS
ROTATING FROM SOUTH TO NORTH THROUGH OUR CWA THEN STALLING NEAR
THE DEFORMATION AXIS INTO THIS EVENING. AFTERNOON HEATING WILL
HELP INCREASE THE LIFT AND STREGHT OF THE SHOWERS I DO NOT AT THIS
TIME PLAN TO ISSUE A FLOOD WATCH AS IT WOULD SEEM ANY HEAVY RAIN
WILL BE RATHER LOCALIZED. STILL WE WILL HAVE TO WATCH THIS.

IT WILL TAKE UNTIL SUNDAY EVENING FROM WHAT IS SEE NOW TO FINALLY
START LIFTING THIS SYSTEM OUT OF THE AREA. SO THAT MEANS I HAVE
EXNTENDED THE SHOWERS INTO SUNDAY. SUNDAY WILL FEATURE DECENT
INSTABLITY SO THUNDERSTORMS ARE ONCE AGAIN EXPECTED. LOCALLY HEAVY
RAINFALL IS ALSO POSSIBLE.

RIDGING BUILD IN SUNDAY NIGHT INTO MONDAY SO SKIES SHOULD CLEAR
AND ALLOW FOR SOME WARMING OF THE AFTERNOON HIGHS BY MONDAY.

.LONG TERM...(Monday night through Friday)

Issued at 308 AM EDT Sat Jul 30 2016
The trend in the forecast for next week is warmer and drier with a
fair amount of sunshine. In general, the upper level pattern will be
defined by ridging through much of next week. 1000-500 mb
thicknesses and 850mb temps will gradually climb Monday night
through Thursday. Highs in the mid 80s should be common Tuesday and
Wednesday, with upper 80s to around 90 degrees more likely for
Thursday.

There are a couple shots at precip next week. The first will be
Tuesday into Tuesday night as a weak shortwave dives southeast
embedded in broad northwest flow aloft. As the shortwave moves
through Chicagoland into northern Indiana, a warm frontal boundary
will be draped across Indiana and Ohio. Will feature highest PoPs
(30 pct) across Southwest Lower.

A better chance for precip will arrive Thursday night and Friday. A
cold front is forecast to move through the state on Friday. This
feature is associated with a closed upper low over Hudson Bay. A
moisture-rich, humid airmass will be in place out ahead of the cold
front as evidenced by a plume of higher theta e extending from the
Gulf Coast states into Michigan. &&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 142 AM EDT Sat Jul 30 2016

MVFR clouds are forecast to expand to all six TAF sites over the
next few hours. Occasional MVFR visibilities will also be
possible, and a heavier shower could result in brief IFR. In
addition to ongoing scattered morning showers, scattered
thunderstorms are possible after roughly 16z Saturday as the
atmosphere becomes more unstable. Winds will continue out of the
east between 5-10 knots over the next 24 hours.

&&

.MARINE...
Issued at 308 AM EDT Sat Jul 30 2016

NORTHEAST WINDS OF 5 TO 15 KNOTS WILL NOT CAUSE MUCH IN THE WAY OF
BEACH HAZARD CONDTIONS. HOWEVER THE THREAT OF LOCALLY HEAVY
SHOWERS AND THUNDERSTORMS WILL BE AN ISSUE THROUGH SUNDAY.

&&

.HYDROLOGY...
Issued at 328 PM EDT Fri Jul 29 2016

Thunderstorms the past two days have primarily been heavy rain
threats, and this will continue to be the case into Saturday. A slow
moving trough with weak vertical shear will continue to promote
isolated to scattered slow-moving storms. No substantial dry air can
be found in the deep convective layer, and precipitable water values
are still around 1.5 inches which is near the 90th percentile for
late July climatology. Slow moving storms Thursday into Friday
produced a number of isolated reports of rainfall greater than 2.50
inches, along with street and parking lot flooding several inches
deep. We will continue to stay alert for the isolated flooding
threat through Saturday.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...EBW
AVIATION...EBW
HYDROLOGY...CAS
MARINE...WDM



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