Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 171734
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
134 PM EDT Thu May 17 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Thu May 17 2018

High pressure over Ontario will continue to provide dry, but
breezy, weather today and Friday before weak low pressure
approaching from the southwest brings clouds and a chance of rain
showers over the weekend.

&&

.SHORT TERM...(Today through Saturday)
Issued at 330 AM EDT Thu May 17 2018

Back door cold front being sent down by the Hudson Bay sfc high
will deliver cooler air to much of nrn Lwr MI and the Thumb
region, but here in sw Lwr MI highs will still be near 80. Coolest
high temps today in the GRR CWFA, around 70, will in the Mt.
Pleasant/Clare areas where strengthening low level northeasterly
flow will bring a cool marine influence in off Lake Huron.

Typically in this regime the highest winds develop in a corridor
from the the Saginaw Valley Region toward Grand Rapids. Some gusts
to 25 MPH seem possible during peak heating. The back door front
will also usher in a drier air mass leading to sunny skies today
and clear/colder tonight.

Look for highs on friday to be about 5-8 degrees cooler than today
due to continued cold advection from the east. High level
cloudiness should begin to increase from south to north in the
afternoon.

Weak upper lows currently over MO/AR eventually merge/consolidate
then lift northeast in our direction Friday night/Saturday. This
helps pulls higher precipitable water values of over 1.5 inches
northward, leading to clouds and scattered rain showers.
Precipitation amounts do not look excessive... with only a tenth
to quarter inch expected at this time. Have restricted any thunder
risk Saturday afternoon to the far southeast around JXN where MU
CAPEs increase to around 1000 J/JG.

.LONG TERM...(Saturday night through Wednesday)
Issued at 330 AM EDT Thu May 17 2018

Timing appears to have changed slightly regarding the exit of the
weekend system. The changes in timing are mainly having to do with
the exit of the system. Model consensus lingers rain into Monday now
with a slower exit compared to 24 hours ago. This trend in the
models is likely due to the upper low being a bit slower to open up
and shift east. We continue to hold on to thunder chances as
instability both at the sfc and aloft is present.

Once the system exits the area by Tue, we are looking at a couple of
very nice late spring days. High pressure will build in the wake of
the departing low. The upper air pattern looks to get a bit
amplified and congested toward mid-week next week. Systems do not
look to move very quick. We could end up in a good spot between the
two branches of the jet with not much moisture expected Tue and Wed.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 134 PM EDT Thu May 17 2018

High confidence for VFR through the period. Wind direction will
become from the east-northeast areawide by late afternoon, but
prior to that they might be variable closer to the coast,
including the MKG and GRR terminals. Do not expect much in the way
of clouds, although a few afternoon cumulus with bases around 5000
ft AGL are possible around JXN.


&&

.MARINE...
Issued at 330 AM EDT Thu May 17 2018

Easterly/offshore flow expected today and Friday, leading to
limited wave action along the coast. Wind speeds could approach
small craft advisory criteria at times south of Whitehall, but
too marginal to issue any marine headlines at this point.


&&

.HYDROLOGY...
Issued at 113 PM EDT Wed May 16 2018

River levels are high across southern Lower Michigan due to the
recent heavy rains. The rivers in central Lower Michigan are near to
a little above normal. A river flood warning continues for the
Portage River near Vicksburg. All other sites are forecast to crest
below flood stage, or have already crested.

Dry weather into Saturday will allow runoff to complete and the
flood crests to move downstream without further enhancement.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...NJJ
AVIATION...TJT
HYDROLOGY...63
MARINE...Meade



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