Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
845 PM CDT Sat Aug 29 2015
clouds will remain locked in overnight under very weak flow and
very moist boundary layer conditions. The main question is whether
we/ll see dense fog develop. Guidance suggest the best chance for
dense fog will be throughout the counties bordering Lake Michigan.
The nearshore waters are quite cool due to some upwelling that
occurred earlier in the week and this is likely resulting in the
very low cloud decks and reduced visibilities there. The Atwater buoy off
of Milwaukee is reporting a 49f water temperature. The persistent stratus
may keep the fog from getting dense...but will keep an eye on it
and Post a dense fog advisory later if needed.
Otherwise...temperatures won't fall too hard tonight with the clouds and
elevated dew points. We should see some clearing later in the
morning on Sunday as the sun helps to mix out the low level
we should see IFR and LIFR conditions expand through the night
due to weak low level flow and very high boundary layer moisture.
Kmke could see LIFR ceilings/visibilities due to the proximity of the lake
and its influence within the light flow regime. Conditions should
quickly improve by 14-16z Sunday morning. Winds will be light
through the taf period.
Will continue the marine dense fog advisory due to the cool waters
within the nearshore waters combining with the elevated dew
points. Conditions should improve by middle to late morning on
Previous discussion... /issued 316 PM CDT Sat Aug 29 2015/
Tonight - confidence...medium
middle level trough axis shifting southeast of WI. Meanwhile the low
levels remain moist with little stirring or change of airmass. A
weak inverted trough extends into WI. Widespread stratus has a
pretty firm grip on central and southern WI. Some breaks and thin
spots have tried to take shape within subsidence region of exiting
shortwave however this has been slow to evolve with overcast conditions
being prevalent. Expecting this regime to change little into the
overnight hours as the column remains free of wind in the surface-
850 millibar layer. Expect fog to become a bit thicker as the night
wears on but confidence not great that widespread dense fog will
become an issue due to the ongoing stratus field. Any breaks that
evolve would expect stratus/fog to fill right back in. With the
cloud cover little temperature dropoff expected.
Sunday - confidence...medium
middle level ridging takes hold with surface high dominating in the low
levels. Again not much stirring so erosion of morning fog/stratus may
be a slow process. 925 thermal trough eases a bit with winds turning
more SW and 850 shows some warming as well. So once the sun breaks
through expect temperatures to get back into the 70s with perhaps an 80 or
two in western County Warning Area where lingering stratus likely to erode soonest.
Sunday night through Tuesday...forecast confidence high.
The upper ridge over the plains will roll over into the Great
Lakes for sun nt and Monday. The surface high will move slightly to the
east of the region with a southerly flow developing. 925 mb temperatures will
rise to 23-24c by late afternoon on Monday which yields highs in the
middle to upper 80s away from the lake breeze. The upper ridge will
flatten and move to the Middle Atlantic States for Tuesday with a southwesterly
flow aloft from the western USA into the northern Great Lakes. It appears
any embedded weak shortwave troughs will remain to the west so the
dry forecast continues. High temperatures middle to upper 80s will continue
except near Lake Michigan.
Long term...Wednesday through Saturday...forecast confidence
The mean upper trough will remain over western Canada and the Pacific
northwest with a broad ridge over much of the central and eastern USA. Weak
shortwave troughs however will flatten the ridge at times and
bring slight chances of thunderstorms to the region from Wed-Sat. Very
warm and humid conditions will continue.
Aviation/00z tafs/...very weak 925/850 flow through tonight and
into early Sunday as well. Subsidence with passing shortwave not
doing much to erode the cloud cover. Rap soundings look to dry
things out later today and this evening but that continues to look
optimistic. Leaning more towards the metmos guidance given present vsbl
imagery/surface observation. Stratus likely to keep visibilities from getting
widespread dense though low levels are more moist due to the recent
rains. But still expecting a good deal of LIFR conditions. The
widespread stratus/fog is likely to persist into Sunday morning.
Then as some weak warm air advection takes hold expecting some erosion to take
place with gradually improving ceilings/visibilities as the day wears on.
Marine...with a light wind regime and a moist airmass remaining in
place have hoisted a dense fog advisory until 10 am Sunday. Fog
will be remain possible at times over Lake Michigan for the new week
due to a humid and stagnant airmass.
Lm...dense fog advisory until 10 am CDT Sunday for lmz643>646.
tonight/Sunday and aviation/marine...collar
Sunday night through Saturday...gehring