Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 201614

Area Forecast Discussion
National Weather Service Northern Indiana
1214 PM EDT Thu Apr 20 2017

Issued at 300 AM EDT Thu Apr 20 2017

A cold front associated with low pressure moving through the
upper Great Lakes will sweep east across our area this afternoon
spawning scattered to numerous thunderstorms. An isolated storm
may be severe this afternoon, mainly over northeast Indiana,
northwest Ohio, and southeast Michigan. High pressure will build
into the area Friday providing fair weather with cooler
temperatures, which will then continue through the weekend.


Issued at 1156 AM EDT Thu Apr 20 2017

Forecast generally on track. Combination of pre-frontal trough
moving in from the west and additional subtle boundary bisecting
the CWA SW to NE, as well as increasing instability should allow
convection slowly expand and organize to some extent over the
next several hours. Best shear presently on (and should generally
remain with) warm front that has pretty much cleared the forecast
area with area well rooted into warm sector. Surface based CAPE of
1000-1500 J/KG in place along/south of the warm front with
slightly higher values along the cold front. HRRR still focusing
development along pre-frontal features which seems right on track
given trends over the past couple hours.

Ramping up of pops into likely range still looks good given
expected coverage. Could argue to go more of a sct to numerous
wording but for now likely mention will suffice. KILX sounding at
12Z showed a decent EML that will settle in this afternoon and at
least help pose a damaging wind threat with the cells that can
gain enough updraft strength and some organization.


.SHORT TERM...(Today and Tonight)
Issued at 300 AM EDT Thu Apr 20 2017

Potent sw trough over wrn MN this morning will continue ewd into the
UP by evening as swwd trailing cold front accelerates ewd through
the great lakes/OH valley as sfc low over central IA migrates newd
into central MI. Ewd portion of sfc boundary currently stalled
through cntrl IL/IN yet will mix rapidly nwd through daybreak
corresponding to ramping low level warm advection. Still expect
convection to fire twd 08Z timed with veering swrly H85 45kt jet and
substantial pocket of theta-e working into nrn zones out of IL.

Otherwise morning period expected to be quiet as low level theta-e
min over ern MO lifts ne and LLJ weakens. Thereafter resurgence of
LLj commences along/ahead of diffuse prefrontal sfc trough within
rapidly destabilizing sfc based airmass. However erosion of eml
along with poor deep layer shear suggest little if any organized
severe risk this aftn. Nonetheless some marginal severe risk is
implied with semi-organized multicell clusters within unidirectional
swrly flow early to mid aftn.

Strong post frontal drying and cold advection surge follows tonight
with a lingering shra chc far southeast early this evening.


.LONG TERM...(Friday through Wednesday)
Issued at 300 AM EDT Thu Apr 20 2017

Trailing sw coming onshore over nrn CA this morning will eject ewd
through the mid MS valley this weekend as strong sfc ridging builds
in across the lakes. Thus expect cool/dry weather will persist

In wake of this sys... energetic pacific wave train consisting of
multiple disturbances will follow next week. Lead disturbance will
minor out through the nrn lakes twd Tue followed by more vigorous
sys developing through the ern corn belt late period. Building mid
level ridging/low level thermal troughing expected ewd across the
lakes/OH valley with substantial temp moderation back to well above
normal by Tue and continuing into/through next weekend.


.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 650 AM EDT Thu Apr 20 2017

Warm front lifting rapidly northeast this morning and lingering
showers/storms will exit within the next few hours. Main concern
will be timing of thunder chances with afternoon cold frontal
passage. Still looks like a mid-late afternoon passage and will
add a bit more specificity to the 12Z TAF`s. Even outside of
convection...southwest winds may gust up to 30 kts at times today
given tight gradient and relatively deep mixing. Other main item
of concern is potential for some postfrontal MVFR stratus. Not
confident that MVFR will persist all night at KSBN given degree of
dry air advection but will hold onto it for now and let day shift


LM...Small Craft Advisory until 11 PM EDT Friday for LMZ043-046.




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