Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 202328 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 628 PM CDT Thu Jul 20 2017 .SHORT TERM...(Tonight through Sunday) Issued at 337 PM CDT Thu Jul 20 2017 Excessive heat maintained a strong grip over the southern 3/4 of the forecast area where 3 PM heat indices were in the 100-110 range. However, a weak slow moving MCV with thicker cloud cover and even a few light showers has at least tempered the heat a bit over far northeast Nebraska. Regardless, even in these areas it has remained hot...just not as hot as it would have been in the absence of those clouds. Expect T/Td/Heat Index readings for the rest of this evening to behave similarly to yesterday with temperatures increasing another few degrees while the dewpoints also increase over much of the area. This is likely to keep the heat index above 105 into the evening hours before a very gradual cool down takes place. The exception, to some extent, will be those cloudier areas in northern parts of the forecast area. Isolated thunderstorm development is also expected through early evening focused immediately ahead of the slowly advancing MCV along a weak front extending from near West Point to near Denison. If storms develop here, there is a small chance for one or two to become strong or perhaps briefly severe although wind shear is on the low end to support any long-duration severe activity and it should remain fairly isolated and relatively short lived. A secondary chance for thunderstorms will develop between 10 PM and sunrise over mainly areas north of Highway 30 with chances increase as you go farther north. This will be in response to an intensifying low level jet which will converge and focused into northeast Nebraska and northwest Iowa. It appears that the LLJ airmass will be quite dry though and the full amount of most unstable energy will not be realized as cloud bases would likely be well-elevated. Thus the potential for severe weather overnight is very low although not completely out of the question if moisture is a bit deeper near/above the LLJ than currently forecast. Friday will be hot once again, and likely very similar conditions to today although with a better chance for the entire area to remain primarily cloud free and hot with the thermal ridge building back into northeast Nebraska. Have thus continued the heat advisory and excessive heat warning areas for the previously issued areas and the heat index forecast has changed very little from the previous forecast. Saturday will start out hot and we`ll have to consider extending heat products for mainly the southeast part of the forecast area. A cold front will be making its way through the forecast area during the daytime hours, and the timing of this front will be the primary factor in just how hot we get on Saturday as the post-frontal airmass should be a good bit cooler than the existing airmass. By Sunday the front will be through the entire forecast area with cooler air filling in. Even with the post-frontal air being cooler, highs will still be in the upper 80s to lower 90s while dewpoints fall into the upper 50s and 60s. Regarding precipitation, there are a few generally low-end chances. The best chances for thunderstorms seem to focus along a weak front and short wave trough in northeast Nebraska on Friday afternoon/evening with another chance mainly near/south of I-80 associated with the cold front on Saturday. .LONG TERM...(Sunday night through Thursday) Issued at 337 PM CDT Thu Jul 20 2017 The long term forecast maintains a fairly similar weather pattern but with a slightly weaker ridge overhead than presently exists. The ridge is also showing tendencies to remain more focused just west of the local area. The end result will be continued hot weather, but the likelihood of another extreme heat event currently appears to be on the lower end. This may allow the weak short wave energy track to shift slightly farther to the south than it has been this week, and while precip chances are low, we will continue to advertise at least low-end precipitation potential through much of next week as multiple weak waves cross the northern Plains and may influence (mainly northern) parts of the forecast area. && .AVIATION...
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(For the 00Z TAFS through 00Z Friday evening) Issued at 618 PM CDT Thu Jul 20 2017 VFR conditions will prevail thru the fcst pd. There is a threat at KOFK though for a brief pd of TSRA shortly after midnight. In addition...threat for LLWS will be in place at all terminals btwn 06z-13z.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Excessive Heat Warning until 8 PM CDT Friday for NEZ034-044-045- 050>053-065>068-078-088>093. Heat Advisory until 8 PM CDT Friday for NEZ015-018-030>033-042- 043. Heat Advisory from noon to 8 PM CDT Friday for NEZ011-012-016- 017. IA...Excessive Heat Warning until 8 PM CDT Friday for IAZ055-056-069- 079-080-090-091. Heat Advisory until 8 PM CDT Friday for IAZ043. && $$ SHORT TERM...Barjenbruch LONG TERM...Barjenbruch AVIATION...DEE

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