Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 191145
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
545 AM MDT Thu Jul 19 2018

.SHORT TERM...(Today through Saturday night)
Issued at 355 AM MDT Thu Jul 19 2018

Main issues will be fog this morning and chances of thunderstorms
through the period. Satellite continuing to show an amplified flow
over the Pacific with a more progressive flow over North America.
Broad and strong ridge aloft continues from the east central Pacific
into much of the western portion of the country then down into the
south central portion of the country. Low levels remain moist.
However, air mass has dried at mid levels from 24 hours ago. Weak
frontal boundary is not too far to the south and west of the area.

Models were close at mid levels with the Gfs, Canadian, and Nam a
little better. The Sref and Ecmwf were starting the best at the
surface. Models started out close/well on the low level thermal
field with Sref, Ecmwf, Nam, and Canadian doing slightly better.

Today/tonight...Air mass remains very moist at low levels with light
winds and little cloud cover. Despite that earlier models runs did
not have any fog. However, now that it is developing they are
starting to grab onto it with the 06z Nam the closest to reality at
this time. Will insert fog into the forecast through mid morning.

As the night has progressed, the Hrrr and Rap have started to
grab onto the idea of thunderstorms developing near 12z and
continuing through the morning, maybe into early afternoon over
the northern and eastern portions of the area. Initially was
skeptical however mesoanalysis is showing a weakening cap in the
area of expected development along with a subtle surface
boundary/convergence. Also shortwave trough moves from the west in
the same time. So have inserted a slight chance of thunderstorms
in the northeast portion through early afternoon.

Question for this afternoon will be if anything can develop. What
makes this even trickier is if something develops this morning
and messes up what the models think is going to happen. Yesterday
had plenty of moisture 700 mb with a surface boundary and a weak
shortwave trough on top of the surface feature, and nothing
developed. Upper air analysis showed an intense EML with 700/500
mb temperatures near +15C/-5C. That effectively capped the low
level air mass.

At the surface models show a surface trough/weak front moving
through the southeast fringe of the area during peak heating time
with the boundary south of the area by 00z. At the same time,
conditions aloft look similar to slightly more hostile to convection
developing. The EML is still in place with the 700/500 mb
temperatures very close or slightly warmer than yesterdays. Am
thinking that we will stay capped like yesterday. Will leave dry for
now with day shift needing to take a closer look at this.

Easterly upslope winds increase through the night in postfrontal
environment, will have to watch for fog developing once again. Did
not put anything in there at this time and will brief the day shift
on this.

Friday/Friday night...Interesting setup with some subtle changes in
the upper pattern/possible conflicts in place. Mid level heights
rise through the day and are higher than they were yesterday or the
day before. However due to the amplifying system over the eastern
portion of the country and a new upper system pushing into the
Pacific northwest and western Canada, the mid level ridge gets
shoved south and east with the center of it to our south and
southeast which could allow subtropical moisture rotate around its
western edge.

700/500 mb temperatures where the models develop thunderstorms, in
the southern third in general, is +16-18/-5C which says the low
levels will be capped. However, there looks to be a more generous
supply of moisture through mid levels. In fact the PWs in the area
in question are 1.5 inches. Combine that with little to no
steering winds aloft will make very heavy rainfall possible.

But what is going to lift this. There is decent low level upslope
winds in place with a very weak shortwave near the southern portion
of the area. Models then transform this into a convectively induced
circulation. There is a hint in the output that there may be a weak
right rear quadrant not too far away.

The new forecast builder has now raised the pops over yesterdays
output into the low chance category. Based on reasoning above I
cannot argue with it. Will be inserting into the HWO the threat for
heavy rainfall.

Wind field/moisture levels will make for a cooler but still muggy
day. The cooler temperatures look fine.

Saturday/Saturday night...The same general setup looks to be in
place with some subtle differences. Southerly winds look to be in
the breezy category, especially in the west. Flow aloft will be
stronger as well as the shortwave trough coming through to lift the
air mass. 700 mb temperatures will be less hot and will be more
favorable to allow thunderstorms to develop with 500 mb temperatures
still -4 to -5C. PWs will be near 1.5.

Thunderstorms look to develop over the higher terrain over eastern
Colorado and then migrate east. However, the current output does not
take these storms very far east into our area. Current builder
output shows this and find it reasonable at this time. However, if
these storms can hold together, they could easily produce heavy
rainfall in our area. High temperatures look to be slightly less hot
and that appears to be fine for now.

.LONG TERM...(Sunday through Wednesday)
Issued at 221 AM MDT Thu Jul 19 2018

A longwave upper-level trough will be centered over the Ohio River
Valley while an upper-level ridge will be centered over Texas and
New Mexico Sunday. This trough is expected to be cutoff and
weaken before dissipating Tuesday, while another upper-level
trough over Saskatchewan progresses eastward. As this second
trough strengthens and dips into the upper Midwest early next
week, the aforementioned ridge will slowly regress back towards
Arizona and California. The ridge and the second trough will work
together to produce relatively strong upper-level winds over the
Central High Plains with generally northwest flow. Several
shortwave troughs coming off the Rocky Mountains will provide some
upper-level forcing for ascent and the possibility for showers
and thunderstorms Sunday night through Wednesday, particularly in
the overnight hours. It is still too far out to determine if there
will be any severe weather potential, but it certainly looks like
there will be above average precipitation across the area
beginning Sunday evening and through the first half of next week.

A cold front passing through the Tri-State Region on Monday will
provide some relief from the scorching temperatures this week as
high temperatures dip down into mid 80s starting on Monday.
Increased chances for showers and thunderstorms should keep
temperatures in the mid to upper 80s through Wednesday. Low
temperatures will also jump down from the mid to upper 60s through
the weekend to the low to mid 60s beginning Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 541 AM MDT Thu Jul 19 2018

For Kgld, winds will be variable in direction at 6 knots or less
through the entire period. Some shallow light fog will burn off
quickly within the first hour. So vfr conditions are expected
through the period.

For Kmck, Ifr conditions will improve to vfr by 15z. Vfr
conditions will continue for the rest of the period. Light and
variable winds at 6 knots or less are expected through the period.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

SHORT TERM...BULLER
LONG TERM...PATTON
AVIATION...BULLER



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