Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Rapids Michigan
1125 PM EDT Friday Oct 24 2014

Latest update...

issued at 327 PM EDT Friday Oct 24 2014

A weak frontal system will move through the area later tonight and
during the first half of the day on Saturday. This front will bring
more clouds in tonight and a chance of sprinkles after a brief
period of clearing late this afternoon and this evening. Clouds will
move out during the day on Saturday and mild temperatures will

The next weather maker will start to make its way in on Sunday night
and early on Monday. Showers and possible storms will move in Sunday
night as another surge of warm air moves up into the area. More rain
will move in for Monday night and Tuesday.


issued at 1120 PM EDT Friday Oct 24 2014

Temperatures dropped off quickly this evening. This...combined
with a humid start to the night allowed for some patchy dense fog
to form. I have added this to the remainder of the forecast for
tonight. Temperatures were also lowered in some areas to account
for the better than anticipated cooling.


Short term...(this evening through Sunday night)
issued at 327 PM EDT Friday Oct 24 2014

No major weather is expected through the short term portion of the
forecast. Cloud trends and the threat of rain tonight will be the first
focus...then transitioning to showers and possible storms for Sunday

We are still expecting a brief window of partial clearing to take
place late this afternoon and evening across the area. Residual low
level moisture with the weakening front has held over the area
through early this afternoon. More breaks are opening up...and we
expect these to expand as the low clouds dissipate and move out.

We have added a chance of sprinkles to the forecast for tonight and
early Sat with the frontal passage. Clouds will move back in
overnight with the approach of the next front currently across the
MO river as of 19z. There is less in the way of upper support with
this next front compared to last night/S front. Short wave energy
and upper jet support both stay well north of the area. Weak ll
moisture transport will be working on a more moist atmosphere
compared to yesterday. We do not expect measurable precipitation tonight or
Sat morning.

The front should begin to move through the area around 12z Sat...and
should exit the County warning forecast area by about 20z or so. Shortly behind the
front...the lower cloud cover should clear out and temperatures should
sneak into the 60s as best cold air advection does not take place until Sat night.
We expect mainly clear skies then through sun evening.

Rain chances will move back in across the northwest half of the County warning forecast area late
on Sun night. The strong system off of the Pacific northwest today will
open up a bit and translate across The Rockies into the plains by
Sun night. This will help to strengthen a warm front to our SW and
drive it in here late Sun night. A decent surge of warmth and
moisture aloft will help to develop showers across the northwest. Thunder
will be possible with elevated Li/S going negative over the area.

Long term...(monday through friday)
issued at 327 PM EDT Friday Oct 24 2014

This period is one of significant changes from the start of the
forecast on Monday to the end of the forecast on Halloween. A strong
Pacific system will bring showers and thunderstorms to the area
Monday into Tuesday. Then we get a good shot of cold air behind the
system for Wednesday only to have a digging northern stream wave
bring the potential for an even stronger cold front in the Thursday
to Friday time frame.

The remnants of extratropical low associated with current Pacific
Tropical Storm Ana now located well northwest of the Hawaiian islands
merges with the Pacific system moving on shore from the Gulf of
Alaska. Typically the models underplay these sorts of systems so I
would imagine what we will actually see will be stronger and slower
then the models currently show. That favors the lower European model (ecmwf) so I
have the best chance for precipitation on Tuesday. Also there is
decent instability (850 Li negative) and the low level jet of 40
knots at 12z near sbn increases to near 50 knots by dtw by Tuesday
evening. When we add the entrance region to a 100 knot 300 mb jet to
the picture and near negative tilt upper trough... I have to believe
thunderstorms are more than possible Tuesday. I put likely probability of precipitation for

That system taps some cold air so we would get some lake effect
showers Wednesday. The real issue is Thursday into Friday. Here we
have 130 to 140 knot jet diving into the already created eastern
trough. How this plays out depend on what happens to the upstream
system over the Gulf of Alaska. Given the much warmer than normal
waters off the coast of southern Alaska and west of British
Columbia... I am thinking that system will be farther west and
deeper so the upstream ridge will be bigger and there will be more
digging into the Great Lakes with this next system for Thursday into
Friday. This should be the coldest weather by far for this season so
far. I did not put snow in the grids yet but do not be surprised if
snow starts showing up the grids for Halloween.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 658 PM EDT Friday Oct 24 2014

The main challenge deals with the timing of the arrival of the
impact conditions tonight for the majority of the taf sites in
southwest Michigan.

IFR and lower conditions are likely to develop over southwest
lower Michigan tonight leading to aviation impacts. The MVFR
conditions continue at kmkg at this time...but could go VFR for a
few hours this evening. However as the entire region cools
off..this will allow for the fog and stratus to
develop...especially after midnight. I am concerned that the
impact conditions could develop sooner than forecasted. Aviators
will need to monitor trends closely through the night and Saturday
morning. Conditions will be slow to improve Saturday...but VFR is
expected to arrive by late morning through middle afternoon.


issued at 1120 PM EDT Friday Oct 24 2014

Wind will be increasing on Saturday...and will likely support the
need for small craft advisories by evening. The flow will be
veering and increasing with time behind the cold front. This will
support some waves bigger than 4 feet.


issued at 327 PM EDT Friday Oct 24 2014

No hydrology issues are expected over the next week. River levels
are starting out around average with the recent dry weather we have
had. We are not expecting any measurable precipitation until at least Sun

There will be a couple of periods of rain next week. Each of these
rain events look to be on the lighter side with only a quarter to
half an inch of rain with each event. These amounts spread out over
the week will not cause any major rises on the area rivers.


GRR watches/warnings/advisories...


short term...njj
long term...wdm

National Weather Service Glossary of Abbreviations