Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220539
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
139 AM EDT Wed Mar 22 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 247 PM EDT Tue Mar 21 2017

A large area of high pressure over northern Minnesota will build
southeast into Lower Michigan tonight and Wednesday. This fair
weather system will draw down from Canada an unseasonably cold
airmass that will persist into Thursday. A warm front will move
into the region Thursday night and which then lifts into Northern
Lower Michigan on Friday. Any mixed precipitation Thursday Night
will turn to rain showers on Friday as the temperatures moderate.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 247 PM EDT Tue Mar 21 2017

The main challenge in the short term deals with the precipitation
type for Thursday night.

The stronger warm and moist air advection that develops Thursday
night will lead to some precipitation developing. There is even
weakness in the stability so the thunder risk is not zero. For
most of the region this should be a rain event. For the northern
locations...Harrison and Big Rapids a risk for freezing rain
exists. The models after 06z Fri have an above freezing thermal
layer with a shallow colder airmass below. I dont see snow in this
timeframe...unless something changes in the models. If the
moisture moves in sooner...when the airmass is colder...a risk for
snow would exist. So basically I trended the period after 06z
toward freezing rain. I will update the HWO and mention a
possibility for slick roads.

The remainder of the short term period looks rather quiet with
high pressure in control of the weather.

.LONG TERM...(Friday through Tuesday)
Issued at 247 PM EDT Tue Mar 21 2017

The main challenge in the long term deals with the precipitation
type for Saturday night. This storm is still out over the Central
Pacific...so much uncertainty exists as to how this system will
evolve...but overall the models are fairly similar with the setup.

The surface pattern with strong high pressure over Ontario and a
weak surface low approaching from the southwest favors ZR for
parts of the region. The forecast sounding from the High Res Euro
for 12z Sunday at Harrison in Clare County is moist and has 850 mb
temps of 4.5 deg C while 925 mb temps are -2 deg C. With the
surface temperature near freezing...this would support a risk for
ZR. The GFS is warmer at that time...but also shows an elevated
warm layer. The GFS shows the shallow cold air in place earlier in
the evening for Saturday and even Saturday afternoon...but that
model is slightly too warm for ZR. Neither model at this point
supports a potential for snow. So I trended the forecast toward
risk for ZR for the interior northern zones for later Saturday
night and early Sunday morning.

Weakness in the stability exists Friday into Sunday...so there is
a small potential for thunderstorms. I did not add thunder to
this period at this time as the risk is rather small and
confidence of exact timing is low. We will need to monitor the
trends closely.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 139 AM EDT Wed Mar 22 2017

Northerly winds will occassionally gust to near 20 kts at southern
TAF sites for the first few hours in the period. Gusts will
become less likely through dawn. Northerly winds of 5-10 kts
Wednesday will likely become light and variable by evening,
calming altogether in some locations.

High clouds will stream in late Wednesday evening. Otherwise,
clear skies and good visibility will result in VFR conditions
through the period.

&&

.MARINE...
Issued at 247 PM EDT Tue Mar 21 2017

The gusty northerly flow along with cold air advection will
continue to support small craft conditions through tonight. The
pressure gradient weakens considerably on Wednesday. That will
allow the winds and waves to decrease steadily.


&&

.HYDROLOGY...
Issued at 247 PM EDT Tue Mar 21 2017

Thursday night into next week is looking like an active period with
multiple opportunities for rain. Rainfall amounts in excess of an
inch by early next week are possible. At this time it`s unknown
exactly where the heavier rain amounts will fall. But this will bear
monitoring, as certain rivers could climb above bankfull if heavy
rain falls within their basins.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until noon EDT today for LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...MJS
AVIATION...JAM
HYDROLOGY...CAS
MARINE...MJS



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