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FXUS63 KLBF 012322 AFDLBF

Area Forecast Discussion National Weather Service North Platte NE 622 PM CDT Wed May 1 2024

KEY MESSAGES

- Strong to severe storms across central and southwestern Nebraska late this evening into the early overnight hours.
Primary threat is large hail, however, damaging wind gusts (60+ mph) cannot be ruled out.

- Brief break from precipitation on Thursday with mild temperatures in the 60s ahead of a second system expected to impact the area on Friday which will bring the potential for strong to severe thunderstorms and locally heavy rainfall.

- Dry conditions return Saturday and Sunday. However, unsettled weather conditions continue next week with additional chances for precipitation and a gradual warming trend bringing high temperatures back to near or slightly above normal. The severe threat remains uncertain at this time.

SYNOPSIS
Issued at 331 PM CDT Wed May 1 2024

Recent GOES-16 WV imagery and RAP 500-mb analysis showed a persistent low pressure system centered across southern Alberta/Saskatchewan with a trough extending southwest into the Great Basin and Desert Southwest. An upper-level shortwave was ejecting off the parent low pressure system, across the Upper Midwest/Great Lakes. A more robust southern stream trough was traversing eastward out of the northern and central Rockies.
Southwesterly flow aloft has continued to increase across the central and southwestern Plains. At the surface, high pressure was noted across the Midwest into portions of the northern Plains. Surface low pressure was apparent across the Texas/Oklahoma Panhandle with a dryline extending southwestward into the Upper Rio Grande in Texas and a warm front was tracking northeastward across central Kansas. Isentropic lift on the northwest periphery of the surface high pressure and multiple weak upper-level shortwaves tracking through has resulted in continued scattered light rain showers across north and north central Nebraska. As the surface high pressure tracks northeastward, this activity should exit the area in the next few hours. Some light to moderate rain showers have also developed across the northwest Sandhills this afternoon in vicinity of an inverted surface trough and weak cold front extending across eastern Wyoming into northwest South Dakota.
However, the main focus for rain showers and a few thunderstorms this evening into the overnight period will occur as an inverted surface trough extends northeastward out of the southern Plains into the area. As of 3 PM CT, temperatures ranged from 51 degrees at Gordon to 61 degrees at Broken Bow.

SHORT TERM /THROUGH THURSDAY NIGHT/
Issued at 331 PM CDT Wed May 1 2024

Tonight...Upper-level lift will increase over the area this evening into tonight as the shortwave ejects across the local area. A complex of storms appears to develop in vicinity of the inverted trough across southwest into central Nebraska, primarily after 00Z.
This complex of storms will move from west to east across the area, exiting the area by ~09Z tonight as the system tracks northeast into the Midwest region. While the main area for severe weather resides further south and east of the area, continuing to see the potential of a brief window for isolated strong to severe storms across portions of central and southwest Nebraska. Elevated CAPE and steep lapse rates aloft will create an environment that will be supportive of large hail and gusty winds for the cores that are able to maintain themselves. The area of concern will be along and south of a SW-NE line from Chappell to Burwell with the greatest threat across Frontier County where the greatest moisture and forcing will set up. Outside of the severe threat, locally heavy rainfall is possible across portions of the southwest Nebraska into northeastern Nebraska. Some uncertainty remains on the placement of heaviest rainfall due to recent CAMs continuing to waver back and forth. However, anticipate this to occur where the strongest ascent is as the low-level jet (LLJ)
noses into the southeastern portion of the state, intersecting the front and MUCAPE >1,000 J/kg. Current thinking is the greatest threat for rainfall amounts of 1 to 2" will reside southeast of a SW-NE line from Hayes Center to Broken Bow to O'Neill. While the threat for flash flooding is low, this will be the area most favorable for heavy rainfall with the possibility of lowland flooding.

Thursday and Thursday Night...Outside of the potential for lingering showers and embedded thunderstorms through the early morning hours on Thursday across north central Nebraska, quieter conditions set up across the area during the day. A strong surge of drier air will push into the area behind the exiting system with surface high pressure centering over central Nebraska. West winds will strengthen as a result with frequent gusts of 25 to 30 miles per hour throughout the day. These gusty winds combined with afternoon humidities bottoming out near 20 percent will introduce elevated fire weather concerns for portions of the area, primarily across the Panhandle into the Sandhills (Fire Weather Zones 204 and 210). Unseasonably cool temperatures are expected Thursday, ranging from the upper 50s across northwest Nebraska to upper 60s across southwest. Chilly air will begin to filter in from the northwest overnight with lows ranging from 30 degrees across northwest Nebraska to 40 degrees across southwest.

LONG TERM /FRIDAY THROUGH WEDNESDAY/
Issued at 331 PM CDT Wed May 1 2024

On Friday, the main upper-level low pressure system will finally begin to move northeastward into Ontario with a trough extending into the northern Plains. At the same time, associated surface low pressure will deepen across Ontario with a strong, attendant cold front advancing out of the northwest across the local area through the day on Friday. A modest 250-mb jet maxima of 100+ kts will orient southwest to northeast from southern Wyoming through southern Minnesota, aiding in upper-level divergence. Robust frontogenetical forcing behind the front resulting in increased cloudiness and a threat for precipitation across much of the area Friday and Friday night. While the greatest moisture and instability will reside further south of the area, the robust forcing combined with steep lapse rates will bring create an environment supportive of severe storms capable of producing large hail and damaging winds for areas generally south of Highway 2. Convection appears to initiate off the Front Range, eventually congealing into a Mesoscale Convective System (MCS)
as it tracks eastward across southern Nebraska. With the potential for the MCS setup, localized flooding will be a concern with current models highlighting modest QPF of 1"+ across portions of southwest Nebraska. Recent rainfall over the last few days has resulted in saturated ground across much of the aforementioned area which will lead to additional concerns for localized flooding. This is highlighted by the Weather Prediction Center (WPC) Day 3 Marginal Risk of Excessive Rainfall Outlook (ERO) across the southern third of the state of Nebraska. Will continue to monitor the severe potential as CAMs get into range and get a better handle on the track of the low and the environment.

As the main system departs eastward early Saturday morning, a return to dry conditions is expected during the day Saturday into Sunday as the upper-level ridge nudges eastward into the Plains. Mild temperatures in the 60s are expected on Saturday, warming into the mid 60s to mid 70s on Sunday. These dry and relatively quiet conditions will be rather short-lived as a strong upper-level low pressure system moving in from the west coast, through the Rockies and into the Plains by the start of next week. This system is very dynamic and may bring a threat for severe thunderstorms to Nebraska on Monday. However timing, location, and degree of the severe threat is uncertain at this time. With the potential for an active period for early next week, make sure to keep up to date with the latest forecasts as details get ironed out with subsequent forecasts.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/
Issued at 622 PM CDT Wed May 1 2024

A storm system working across the Great Plains will result in a few aviation weather concerns for western and north central Nebraska terminals through the forecast period. Showers and thunderstorms will continue pushing east across the northern terminals (VTN) early this evening, while new storms will develop across the southern terminals (LBF) later this evening.
Erratic gusty winds, reduced visibility, and low ceilings are all expected at times through at least 02/06z. A low stratus deck may work into the region overnight, further lowering cigs into IFR. Southeast winds will transition to west/northwest by mid-morning, which will help clear the clouds out throughout the day tomorrow. Northwest gusts will approach 25 kts.

LBF WATCHES/WARNINGS/ADVISORIES
None.

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