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Area forecast discussion 
National Weather Service Grand Rapids Michigan
1243 am EDT Wednesday Aug 20 2014

Latest update...

issued at 330 PM EDT Tuesday Aug 19 2014

Thunderstorms with heavy rain and gusty winds will exit tonight as a
cold front passes through but a few scattered showers will linger
tonight and Wednesday.

A strong warm front will approach from the southwest Thursday and
Thursday night. This front may trigger another round of heavy
thunderstorms... followed by very warm and humid conditions for the
upcoming weekend.


Short term...(this evening through Thursday night)
issued at 330 PM EDT Tuesday Aug 19 2014

Active weather will continue over the next few hours as approaching
cold front over eastern WI interacts with very moist and unstable air
mass over Southern Lower Michigan. Convective available potential energy are 1500-2000 south of I-96 with upper 60
dew points and precipitable waters around 1.7. There have been some reports of
torrential rain with more than two inches an hour... so Urban and
Small Stream flooding is a threat in addition to the threat for
severe/weather damaging winds.

Rain chances decrease later this evening after frontal passage but as the
upper low over western Upper Michigan moves to Northern Lake Huron look for scattered
showers to persist. These may perk back up to thunderstorms on Wednesday
afternoon with heating...particularly over northern and eastern lower Michigan. A
Lake Shadow will probably develop for Wednesday afternoon with northwest
low level flow so will feature a dry afternoon for the coastal
counties while going with likely probability of precipitation for Clare... Montana pleasant...
and Alma areas.

Best probability of precipitation in later periods looks to be Thursday night as the warm
front/low level jet shift toward the area. Guidance...especially the
European model (ecmwf)...looks rather aggressive so there could be a round of strong
storms with heavy rainfall.

Long term...(friday through tuesday)
issued at 330 PM EDT Tuesday Aug 19 2014

It would seem we do actually have a chance of seeing highs near or
above 90 degrees over a good part of our County Warning Area through the weekend
into early next week. As the warm air surges in we will likely have
some significant rainfall (strong thunderstorms) Friday possibly
into Saturday. The next threat of thunderstorms is Monday night
into Tuesday as a cold front moves into the area.

The models are in good agreement on the building of a significant
upper level ridge over the east central sections of the Continental U.S. This
coming weekend. This is in response to strongly digging upper low
over the Pacific northwest in the same time frame. A significant
slit in the upper level jet will keep the cold air north James Bay
through the weekend. The only real issue with the long range
forecast is how quickly the upper low ejects into the plains.
Typically the models do this to quickly. Already the models have
slowed down nearly a day with the cold front coming through.

My forecast highs are based on my 1000/925 mb thickness tool...which
are largely 2 to 4 degrees above most of the MOS numbers. Given
climatology would have an impact on those number... having highs increased
seems like a good idea. That being so we may see our first 90+ highs
Sat...sun and Monday. I have 90 on Sat for now but I would think it is
more than likely Sunday and Monday too.


Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1242 am EDT Wednesday Aug 20 2014

IFR and LIFR conditions expected overnight as significant low
level moisture results in stratus and fog formation. Most sites by
10z-11z should see visibilities at or below 1 mile and ceilings below

The stratus and fog should gradually lift through the course of
the morning with VFR returning in the 15z t0 18z time frame.
Scattered showers are expected Wednesday afternoon...but with far
less coverage and much less intensity. Used vcsh wording for now.

VFR conditions should then prevail into Wednesday evening.


issued at 330 PM EDT Tuesday Aug 19 2014

Generally weak gradient expected so winds and waves should remain
below small craft criteria. However areas of fog will be a
possibility as humid air interacts with the cooler Lake Michigan waters.


issued at 330 PM EDT Tuesday Aug 19 2014

Heavy rainfall rates of 1-2 inches per hour through early evening
will support a threat of Urban and Small Stream flooding. Scattered
nature of these heavier amounts should limit extent of rises on the
larger rivers. The pattern later in the week supports additional
heavy rainfall events so river flooding could become more of a
concern by that time.


GRR watches/warnings/advisories...


short term...Meade
long term...wdm

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