Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Rapids Michigan
1159 PM EDT Monday Apr 27 2015

Latest update...

issued at 330 PM EDT Monday Apr 27 2015

High pressure will bring clearing skies and diminishing winds
tonight... followed by partly to mostly skies for Tuesday. A weak
cold front will drop through on Wednesday night...bringing a few
light rain showers and halting any warm up from occurring until the


issued at 905 PM EDT Monday Apr 27 2015

At 0050z rgnl infrared Sat trends show a fair amount of low cloud cover
continues to advect in from the north-northeast. A consensus of 12z/18z short
range guidance forecasts suggests that some of this cloud cover will
likely linger overnight across portions of our area. 12z met/mav
numerical guidance numbers generally suggest min temperatures will bottom
out in the middle 30s across most of the advisory area.

Given infrared Sat trends and latest numerical guidance conditions for
frost formation look marginal. However given potential for at
least some patchy frost in typically colder locations where the
most clearing occurs we decided to leave the frost advisory
headline unchanged.


Short term...(this evening through Wednesday night)
issued at 330 PM EDT Monday Apr 27 2015

First issue in the short term is frost potential tonight. The
surface ridge currently to our west will be building in which should
lead to diminishing winds and clearing skies. This creates a better
set up for frost than the last couple night so will issue a frost
advisory for the ten counties in SW Michigan where the growing season has

The other issue is the increasing model trend for having another
upper low impact the area Wednesday and Wednesday night. This
feature drops in as an open wave from the northwest on Wednesday
then closes off as it moves south through the area Wednesday night.

Despite our dry air mass it seems reasonable to believe that some
scattered light rain showers will occur with the upper low Wednesday
afternoon and night... especially east of Highway 131.

There will also be a surface cold front or trough passing through
Wednesday night... and models show 800 mb temperatures falling to -2c again
behind it. Obviously this halts our expected warm up until the

Inbetween our departing upper low and the next one... shortwave
ridging is prognosticated for Tuesday. This should result in less cloud
cover than today along with light winds and milder temperatures. Highs in
the lower 60s expected for most areas although lake breezes should
develop/strengthen at the coast in the afternoon leading to much
chillier conditions.

Long term...(thursday through monday)
issued at 330 PM EDT Monday Apr 27 2015

A fairly deep upper low moving over Lake Michigan early Thursday
will remain close enough to the County Warning Area to create the potential for a
few showers...but confidence is low on that since the strongest
dynamics will already be southeast of of the County Warning Area.

A weak cold front is still forecasted to move across the County Warning Area Saturday
toward northern Indiana and then moving north again Sunday. This
will keep low chances of rain...but probably not the
forecast over the weekend. A higher chance of showers and
thunderstorms will come Monday when a stronger cold front approaches
from the west. Instability and a southwest flow of moisture will
move over the County Warning Area. We have thunder in the grids Monday for this

Temperatures will be mostly in the 60s during this period but push
70 Sunday and Monday.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1156 PM EDT Monday Apr 27 2015

Clouds have in fact cleared or are clearing as expected this
evening. The upper level ridge moving into the area from the west
will help the cause. There are clouds trying to back feed from
western Ontario and Northern Lake Huron into lower Michigan but
west edge of the clouds keep eroding eastward as the clouds try
to move in. Bottom line I expect largely clear skies at all taf
sites through the early morning hours of Tuesday.

I do expect cumulus clouds to develop late this morning and with
the light winds and Cold Lake waters... a lake breeze should
develop and keep the cloud from going broken at Muskegon. The
other taf site should see a few hours of broken VFR ceilings due to
day time heating clouds that will dissipate at sunset.


issued at 330 PM EDT Monday Apr 27 2015

North-northwest winds of 20-25 knots will diminish and become offshore later
this evening. Until then small craft advisories remain in effect.
Another strong north flow event... like today and Sunday... looks
likely on Thursday.


issued at 1044 am EDT Monday Apr 27 2015

Rivers across southwest lower Michigan are around normal levels
and steady or slowly falling. With dry weather forecast this
week... these trends should continue through the weekend.


GRR watches/warnings/advisories...
Michigan...frost advisory until 9 am EDT Tuesday for miz050-056>058-064>066-



short term...Meade
long term...04

National Weather Service Glossary of Abbreviations