Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 201818

Area Forecast Discussion
National Weather Service Gaylord MI
218 PM EDT Sat Jul 20 2019

Issued at 1121 AM EDT Sat Jul 20 2019

Morning composite analysis reveals a convoluted surface pattern
across the region, muddied by overnight and ongoing convection.
But an inverted surface trough stretches from the central Plains
northeastward to western Wisconsin with a somewhat stationary
boundary then stretching eastward into northern/central Lower
Michigan. SPC analysis reveals a tongue of steep lapse rates aloft
and respectable instability along and south of that boundary that
has been surging back toward lower Michigan over the last several
hours in the wake of the overnight convection. Thin line of
training thunderstorms have been developing along that boundary
and instability gradient across portions of west-central Lower
Michigan and back across the lake over the last few
hours...largely just south of the forecast area.

Further upstream, a couple storm complexes are making their way
across Minnesota and just into western Wisconsin, with some
expansion of convection eastward along the boundary.

An active afternoon/evening appears on tap for at least parts of
the forecast area. Per radar trends, ongoing thin line of
showers/storms into west-central Lower Michigan will likely
continue to develop and train through that region over the next
few hours anyway while bowing back into the SW/southern part of
the forecast area. I`ve adjusted/increased PoPs/QPF through those
areas accordingly. Will also have to keep an eye on severe/flash
flooding potential with those storms heading into the afternoon.

Meanwhile, upstream activity pressing into Wisconsin will
continue to track eastward along the instability gradient/boundary
with trends and recent CAMs suggesting convection grows upscale
and eventually tracks through a chunk of northern Lower Michigan
this afternoon into early evening as bowing line of storms.

Severe weather potential: Yes. Strong evidence to support a
slight to marginal severe storm risk for the southern half of the
forecast area through the afternoon into early evening with MUCAPE
values climbing to near 4000 J/KG (already over 2500 on the
morning APX sounding). Unclear how much MLCAPE we will realize
from heating given the amount of cloud cover that is and likely to
remain draped through the region. But given the amount of
instability aloft and strong mid level flow (40 to 50 knots at 500
MB) supporting organized storms, it`s enough to be concerned for
the potential of damaging wind gusts and large hail. Heavy
rainfall is a given in this airmass.


.NEAR TERM...(Today through Tonight)
Issued at 412 AM EDT Sat Jul 20 2019

...Heat and Storms...

High Impact Weather Potential: Severe storm potential south of M-72
this afternoon/evening with main threat damaging winds.  Heat
indices near triple digits in the counties near Saginaw Bay.

Pattern Synopsis/Forecast: A quasi-stationary frontal boundary
extends from south-central Minnesota into western upper Michigan
this morning.  The airmass south of this feature remains very warm,
moist and unstable.  The boundary will make slow southward progress
today as additional mid level shortwave energy slides eastward along
it.  This will result in additional showers/storms for parts of
northern Michigan.

Somewhat of a difficult forecast with regard to precipitation
chances and temperatures as front sags slowly southward through the
area this afternoon and evening.  Airmass should recover fairly
quickly in the wake of the convection overnight.  Plenty of
instability, low level moisture and favorable kinematics with strong
mid level wind fields to generate additional showers/storms south of
the boundary into this evening.  Main severe threat today will be
south of M-72 (highest along and south of M-55) where low level
moisture convergence with align best with warm temps/high dewpoint
air.   An approaching mid level wave out of Wisconsin will bring the
added forcing necessary to produce an uptick in coverage of
showers/storms (mainly northern lower) later this afternoon and
evening. Additional upstream energy may keep at least a few
showers/storms going across parts of the area overnight.

Another hot and humid day for many areas although gradually drier
air will seep in from the north as the day progresses (making for a
slightly more comfortable day for the northern 1/2 of the area).
Currently have heat advisories in the counties closet to Saginaw Bay
and this appears to be the most likely area to see heat index values
approach triple digits.  So have no plans to extend the advisory any
further north/west than it is currently.


.SHORT TERM...(Sunday through Monday)
Issued at 412 AM EDT Sat Jul 20 2019

High Impact Weather Potential...Minimal

Pattern Synopsis/Forecast...The models are showing the front from
today hanging around the center of the lower peninsula with rain
north and south of the front. The only thing about that is that some
models are showing rain as far north as M-68 or M-32, while others
are as far south as M-55 or US-10. So far it looks like it will
depend on the MCS production over the next 24 hours, and the
reinforcement of the cold pool keeping warm front south of the
forecast area. The SREF is of little help as it has rain from ANJ,
to the Ohio Border. So the general feeling is for the front to
stay south Sunday morning, and continue to push south and stay
south through Monday morning. Monday looks dry as well, especially
as the 500 mb trough pushes through the forecast area with all of
its mid level dry air. However, there could be some cloud issues
as the 850 mb moisture remains high and the GFs shows some
potential for a cu or stratocu field to develop and keep us a
little cooler than thought, but the ECMWF is drier through Monday,
so will lean toward the consensus grids for the time being.

Primary Forecast Concerns...Main concern will be the chances for
rain Sunday morning/afternoon as the front pushes south. As
mentioned before, if the convection allowing models are right,
little rain will happen, and the cold pool will push the front
south, and maintain it south, allowing high pressure to build into
the region.

.LONG TERM...(Monday night through Friday)
Issued at 412 AM EDT Sat Jul 20 2019

High Impact Weather Potential...Minimal this week

Extended (Tuesday through Friday)...The 500 mb trough just to the
east, we get into Northwest flow into Thursday morning, which
produces showers on and off as each impulse of energy drops into the
bottom of the trough. Thursday the 500 mb trough begins to lift a
bit, but by Friday evening, the next impulse moves into the region
and showers and thunderstorms will be possible Friday night.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 218 PM EDT Sat Jul 20 2019

Complex of thunderstorms will cross northern Lower Michigan this
afternoon, primarily impacting MBL and TVC with lesser impacts for
PLN and APN. Convection should exit the area early this evening.

Cloud cover trends remain nebulous at this point. A fair amount of
lower cloud cover has developed across northern Lower Michigan
bringing a large amount of MVFR cloud cover to the region. That
will likely remain the case through the afternoon...possibly into
the evening as the rainfall moves through.

Will see how well we can thin out the cloud cover tonight behind
the storm complex. Right now, I have the terminal sites returning
to VFR weather...but that may change.

VFR weather will return to the area on Sunday.


Issued at 412 AM EDT Sat Jul 20 2019

A very warm and humid airmass will continue across the
Great Lakes region today, bringing additional chances for showers
and storms. There remains a chance for a few severe storms,
primarily this afternoon and evening.  Winds will be a bit gusty
today as a cold front slowly sags southward through the area.
Will not hoist any advisories for the nearshore areas today but
occasional gusts could approach advisory levels. Quieter weather
for Sunday into the the first part of next week with high pressure
in control.




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