Area Forecast Discussion
Issued by NWS Gaylord, MI

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276
FXUS63 KAPX 220353
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1153 PM EDT Fri Jul 21 2017

.UPDATE...
Issued at 825 PM EDT Fri Jul 21 2017

Updated the forecast to lower chances for seeing rain
tonight...and even into Saturday. A stationary front is well south
and west of nrn Michigan, where the moisture and instability
gradient resides. Showers and thunderstorms have fired along and
north of this front, in association with a weak shortwave trough
and 35-40kt LLJ which is out of the WSW. This LLJ will only veer
more westerly through the night, limiting any northward advection
of moisture and instability. The weak shortwave trough does arrive
after midnight, while there are indications of low pressure
sliding into srn Lake Michigan. This could bring a isolated to
scattered light showers to nrn Michigan, but thunderstorms look
unlikely. This low pressure pushes eastward across srn lower
Michigan Saturday and Saturday night, taking any showers eastward
through the day. However, light cyclonic flow Saturday is likely
to lead to lake breezes and maxed convergence more so across NW
lower Michigan for another basically small chance for showers and
thunderstorms. An inverted trough axis from the low pressure
lingers back across nrn Michigan Saturday night while a more
defined shortwave pushes into the region overnight. This will
likely bring the better chances for seeing rainfall and maybe a
few storms.

&&

.NEAR TERM...(Tonight through Saturday)
Issued at 255 PM EDT Fri Jul 21 2017

...Small chances of thunder late tonight into Saturday...

High Impact Weather Potential...

Pattern Synopsis/Forecast...Narrow ridge of high pressure still
extends from Western Ontario thru Michigan this afternoon. Low
pressure continues to develop over the Northern Plains...with an
associated warm front extending from the low thru Iowa southeastward
into the Ohio Valley. Area of convection continues to fire just
ahead of the surface low and north of the warm front...with
additional convection moving thru West Virginia. Back in Michigan...
mid/upper level clouds from upstream convection are spreading from
west to east into our area as the warm front slowly lifts toward the
Western Great Lakes region.

As we head into tonight...latest NAM continues to trend slowly
southward with the instability gradient and higher 850 mb theta E
ridging...keeping best path for upstream convective propagation
south and west of our CWA thru the SW half of Wisconsin into into
Southern Lake Michigan and SW Lower Michigan. Certainly do not think
this will keep our CWA high and dry by any means...and have keeps
increasing POPs in the forecast for tonight into Saturday. Highest
POPs and chances of thunder will be across the SW half of our
CWA...tapering to chance across our NE CWA. Latest SPC Day 1 Outlook
has our entire CWA in general thunder...and think this is very
reasonable.

With increasing clouds and continued WAA...low temps will only cool
into the 60s tonight. Temps will be a bit cooler tomorrow given
additional cloud cover...with high temps warming into the upper 70s
to around 80 degrees.

&&

.SHORT TERM...(Saturday night through Monday)
Issued at 255 PM EDT Fri Jul 21 2017

...Showers and storms possible at times through Sunday evening...

High Impact Weather Potential...Thunderstorms possible Sunday
afternoon/evening.

Pattern Synopsis/Forecast...Digging upper shortwave trough will drop
into the Upper Great Lakes region through Sunday until a building
upstream ridge nudges it eastward on Monday. Meanwhile a weakly
organized surface low will meander from the southwest corner of
Ontario to western New York by Monday morning as a strong surface
high and drier air settle into the Upper Midwest, ending the rain
chances.

Primary Forecast Concerns...Extent of showers Saturday night into
Sunday and storm potential Sunday afternoon will be the main
forecast challenges. The 21.12Z GFS develops a deeper
shortwave/cutoff low with less southward extent than other synoptic
models. Hard to go with the outlier given other models` good
consensus, but the GFS may have the right idea in terms of a slower
system given the ridge strengthening upstream and the 21.12Z ECMWF
just came in with a similar solution. At any rate, forcing looks to
gradually ramp up Saturday night into Sunday as this system moves
into northern MI. Plenty of moisture available with forecast
soundings getting close to saturation in the low levels Saturday
night into early Sunday. That will limit instability, however, as
low level lapse rates will be rather weak. Thus, expecting mainly
just scattered showers into Sunday morning. As the surface low
migrates across northern Lower during the day Sunday, it will likely
pull a plume of higher theta-e air northward into the area, leading
to somewhat better diurnal instability. This will allow for a chance
of thunderstorms during the afternoon and evening hours. Shear will
be pretty weak in vicinity of the surface low, but wouldn`t
completely rule out the possibility for a marginally severe storm
mainly across our southern counties where instability will be
relatively higher.

High pressure and drier air building in from the west Sunday night
will bring an end to any lingering rain activity by late evening.
Cool northerly flow will lead to highs in the low to mid 70s on
Monday.

.LONG TERM...(Monday night through Friday)
Issued at 255 PM EDT Fri Jul 21 2017

Long range guidance is in good agreement with the extended period
beginning with surface high pressure over the Great Lakes region
providing rain free and warm weather through Tuesday evening.
Tuesday night thru Wednesday night will see a return of rain/thunder
as a cold front associated with a low pressure system over James Bay
sweeps through the forecast area. High pressure then builds back
into the area behind the departing system, returning partly cloudy
skies and rain free weather through Friday. Daytime highs will be in
the upper 70s to low 80s, while lows will dip down into the mid to
upper 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1147 PM EDT Fri Jul 21 2017

Only some patchy light rains and light winds expected tonight as
weak high pressure drifts east and low pressure moves into srn
Lake Michigan. Better chances for seeing a little light rain will
be from MBL to APN into Saturday morning. The low pressure then
crosses srn lower Michigan through Saturday and Saturday night.
Winds remain light and more variable Saturday tending to lake
breezes. Best convergence will be across NW lower where some
additional showers and maybe isolated storms may develop. Still
too low of a chance to include in the TAFS. A better chance
arrives Saturday night with the arrival of a stronger disturbance
aloft, and sfc troughing laid out across nrn Michigan. VFR through
the period.

&&

.MARINE...
Issued at 255 PM EDT Fri Jul 21 2017

Winds and waves will remain below SCA criteria through the weekend.
Chances of shower and storms will increase for much of our tonight
ahead of low pressure developing over the Northern Plains. Chances
of precip will remain in the forecast thru the weekend as this low
tracks east through the Great Lakes.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...SD
NEAR TERM...MR
SHORT TERM...MK
LONG TERM...TL
AVIATION...SD
MARINE...MR



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