NWS-GRR Issues Area Forecast Discussion on Fri, 29 May 2020 06:27:00 EDT

Fri, 29 May 2020 14:26 GMT
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Here is the forecast discussion for Today through next Thursday
Issued at 322 AM EDT Fri May 29 2020

-- Showers end today and cooler-- 

Expect an area of rain or rain showers to move through our area 
this morning. The rain is associated with the digging upper 
trough, just behind the surface cold front. There is not enough 
instability for thunderstorms with this rain area and the rain is 
not expected to all that heavy either. The area of rain will be 
east of our CWA by noon for give or take an hour. 

Scattered rain showers are possible this afternoon over or eastern
CWA. The showers for not thunderstorms are associated with fairly 
strong shortwave moving through the area during the midday hours. 
By the time the shortwave moves through this area, the moisture 
is expected to be rather shallow for less than 10000 ft, so any 
showers that do develop will not have much depth. Even then they 
would mostly on the east side of Lower Michigan, closer to I-75. 

More than anything it will be cooler today, it would seem to me
highs should struggle to get to 70 today, which is below our 
normal high which is now in the mid 70s. The 1000 to 925 mb 
thickness tool from the NAM for GFS and ECMWF strongly support this 
idea. In fact the 00z ECMWF ensemble forecast high for GRR today
has only 1 member out of 50 that gives GRR a high over 70 degrees. 

-- Much cooler Saturday and Sunday--

There is a digging northern stream jet core, coming straight 
south from northern Hudson Bay today. It starts to phases with
Pacific origin jet core on the primary branch of the polar jet by
this evening. This strongly digs the upper trough and by Saturday
evening, the primary jet core is south of Michigan. This puts us 
in the deep cold air. Also this brings down the coldest air we 
would typically see at this time of year. The SPC sounding 
database for DTX shows the lowest 850 mb temperatures at this time
of year between 0c and -5c, the models give 850 temps Saturday 
evening near 0c. The ECMWF ensembles for 50 members are tightly 
clustered around 0c Saturday evening for 850 temperatures near 0c.

An issue to consider with this cold of air and with the polar jet
south of us is the potential for afternoon showers. This is shown
by the GFS in fact. During the winter, this would mean lake 
effect snow showers all day Saturday. Since it's the end of May, I
am thinking cumulus clouds inland on Saturday. A stray sprinkle 
would not be out of the question inland of US-131 on Saturday. 

Highs should struggle to reach the lower to mid 60 both Saturday 
and Sunday. Again this is strongly supported by the ECMWF 
ensemble high temperature forecast and also by both the GFS and 
ECMWF operational model 1000 to 850 and 1000 to 925 mb thickness 
forecasts. 

The result of this cold of air is we more than likely will be 
cold enough for some frost Saturday and Sunday morning near and 
north of Route 10. Skies should be able to clear both nights but
more so Sunday morning since the upper trough is moving east by
then. It would seem there should be enough mixing to keep lows 
above freezing but we will have to watch this closely.

-- Warming to near normal next week with showers possible--

Meanwhile we have a progressive upper wave pattern and that brings
a 160 knot jet core to the International Dateline by Sunday night.
That in turn kicks out the current upper trough over the west
coast and that tops the upper ridge over the central plains
Monday. It then dives into the eastern trough Tuesday. This brings
our next chance for showers and thunderstorms. This is a fast
moving system and will not have time get much Gulf Moisture. Also
it seems more of the energy will be over northern Michigan so I 
do not see this as a big rain maker Monday night into Tuesday. 
Still there could be thunderstorms.

The glitch is that the 160 knot jet core reaches the west coast 
Wednesday for more or less. Typically that sort of energy builds a 
deep trough upstream as it moves over the western Mountains. That 
could set up a wet pattern for us later next week or into the 
weekend. However, most of the ensemble members suggest that 
trough will not move this far east all that fast. That being so, 
we might have a nice weekend for the 5th through the 8th of June. 
Here is the aviation discussion for For the 12Z TAFS through 12Z Saturday morning
Issued at 623 AM EDT Fri May 29 2020

IR loop shows a steady eastward progression of the back edge of
the cloud shield as it moves over eastern WI. At it's current
pace, the back edge would clear JXN by 18z. Light rain will also
end mid morning. Look for cigs to increase by mid morning to VFR
at the western terminals and by 20z or so at the eastern taf
sites. 




Here is the marine discussion 
Issued at 322 AM EDT Fri May 29 2020

We did give some through to a Small Craft Advisory for later 
today into Saturday as the cold air comes in. However it looks 
like the winds and waves will not be high enough to meet criteria.
Still we do have 20 to 25 knots in the boundary layer with cold 
air advection, and the air being cold enough of neutral stability 
it is something we will continue to watch.




Here is the hydrology discussion 
Issued at 320 AM EDT Thu May 29 2020

The Grand River at Robinson Twp while still slowly falling was the
only forecast point that has a river flood warning out. Most
streams on the USGS page are either near record or in the much
above normal class as of 2 am this morning. To say the least, our
ground is near saturated. Even so, while we will see a little more
rain this morning it should not be enough to impact creeks or
rivers. Then it will be dry into Monday so rivers and creeks
should continue declining into early next week. 

There is some question how much rain will fall in our area next 
week but at this point it does not look like much more than an 
area wide half inch sort of event mid week. That being so, we 
should not see much in the way of added flooding.
NWS Forecast Office Grand Rapids Michigan Issues Area Forecast Discussion at Fri, 29 May 2020 06:27:00 EDT

NWS-GRR Issues Area Forecast Discussion on Fri, 29 May 2020 06:27:00 EDT
