textproduct: Great Falls

KEY MESSAGES

- Turning drier and much warmer through the weekend, with some record heat possible over the weekend.

- Breezy conditions Saturday may result in some elevated fire conditions, most notably across Southwest Montana

- Not as hot next week, but still warm through next week.

DISCUSSION

- Meteorological Overview: Upper level ridging will bring the warmest temperatures of the year thus far to Southwest through North Central Montana this weekend and into the day on Monday, with overall dry conditions expected through the timeframe. Friday will be the transition day as upper level riding amplifies over the Central Rockies and Northern High Plains, with temperatures warming into the 80s to low 90s. Enough moisture streaming northeast within the upstream side of the amplifying ridge will help to support isolated showers and storms across the Northern Rockies on Friday, initially across Southwest Montana during the afternoon hours before spreading north to Central and North Central Montana during the evening hours. High temperatures warm further into the 90s to low 100s over the weekend and into Monday, with breezy south to west winds developing each day during the afternoon hours, especially across Southwest Montana and along the Rocky Mountain Front. - Moldan

Upper level flow will shift to more westerly on Monday, which will allow temperatures to lower a bit from the weekend highs, but most areas will still be quite warm with temperatures well into the 80s to low 90s. With this upper level flow pattern, expect generally dry conditions with just a few showers and thunderstorms to pop up in the afternoon. A passing upper level trough may bring some more widespread showers and storms on Wednesday, though timing of the trough passage will ultimately determine just how widespread and intense the storms will be. - Ludwig

- Forecast Confidence & Scenarios:

Hot Temperatures this Weekend...

Climate anomaly indicators continue to support the potential for an unusual to very unusual period of hot temperatures, with respect to early to mid-July climatology, across the Northern Rockies; especially along and east of a Lewistown, to Helena, to Chief Joseph Pass line where EFIs are in excess of 0.6. This is not to say that areas north and west of this line will not also see hot temperatures, but with respect to July climatology readings will not be as anomalous.

The tables below depict Low End (NBM5.0 10th Percentiles), Most Likely (50th Percentiles), and High End (NBM5.0 90th Percentiles) scenarios with respect to high and low temperatures over the weekend; with larger spreads between the three scenarios suggesting greater uncertainty due to a combination of cloud cover/wind speeds and directions/latent heat release while smaller spreads suggest greater certainty.

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Saturday's High Temperature Scenarios LOCATION Low End | Most Likely | High End Browning 81 | 84 | 89 Cut Bank 87 | 91 | 95 Havre 94 | 100 | 104 Great Falls 94 | 99 | 103 Lewistown 92 | 96 | 99 Helena 93 | 98 | 101 White Sulphur Springs 92 | 94 | 97 Bozeman 95 | 97 | 99 Dillon 91 | 95 | 97 Ennis 92 | 95 | 97 West Yellowstone 83 | 89 | 91

Sat. Night's Low Temperature Scenarios LOCATION Low End | Most Likely | High End Browning 53 | 57 | 61 Cut Bank 53 | 57 | 64 Havre 57 | 60 | 65 Great Falls 56 | 61 | 66 Lewistown 54 | 57 | 61 Helena 57 | 64 | 67 White Sulphur Springs 52 | 56 | 59 Bozeman 56 | 61 | 64 Dillon 54 | 58 | 61 Ennis 56 | 59 | 62 West Yellowstone 46 | 51 | 56

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Sunday's High Temperature Scenarios LOCATION Low End | Most Likely | High End Browning 79 | 87 | 93 Cut Bank 86 | 93 | 99 Havre 95 | 101 | 109 Great Falls 94 | 100 | 107 Lewistown 94 | 100 | 106 Helena 94 | 99 | 106 White Sulphur Springs 93 | 98 | 102 Bozeman 96 | 101 | 104 Dillon 92 | 97 | 101 Ennis 96 | 100 | 102 West Yellowstone 90 | 94 | 96

Sun. Night's Low Temperature Scenarios LOCATION Low End | Most Likely | High End Browning 52 | 59 | 65 Cut Bank 53 | 61 | 68 Havre 57 | 63 | 69 Great Falls 59 | 64 | 70 Lewistown 55 | 58 | 65 Helena 61 | 67 | 72 White Sulphur Springs 54 | 57 | 63 Bozeman 57 | 61 | 66 Dillon 57 | 61 | 64 Ennis 57 | 60 | 64 West Yellowstone 49 | 55 | 60

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Monday's High Temperature Scenarios LOCATION Low End | Most Likely | High End Browning 79 | 86 | 91 Cut Bank 82 | 91 | 96 Havre 86 | 96 | 103 Great Falls 88 | 97 | 101 Lewistown 85 | 93 | 98 Helena 89 | 95 | 100 White Sulphur Springs 88 | 94 | 97 Bozeman 90 | 96 | 101 Dillon 88 | 93 | 97 Ennis 89 | 95 | 99 West Yellowstone 87 | 92 | 96

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At this time these scenarios continue to suggest that while daytime temperatures will be hot across most areas, especially on Sunday, temperatures will cool sufficiently enough during the overnight hours to provide some relief from the Extreme Heat that will be seen further east over Eastern Montana. This relief offsets the need for Extreme Heat Warnings; however, with overnight lows only dipping into the 60 to 70 degree range across most of the plains and valleys of North Central through Southwest Montana, which is 10 to 15 degrees warmer than climatology, the window for relief will be quite limited. For this reason a Heat Advisory was deemed the most appropriate at this time, but should high and/or low temperatures trend warmer over the next several day then upgrades to Extreme Heat Warnings may be need for some areas. - Moldan

AVIATION

09/18Z TAF Period

VFR conditions will prevail through the 0918/1018 TAF period; however, hot temperatures through the weekend may result in some high density issues, particularly across the terminals of Southwest and portions of Central Montana. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 55 94 59 98 / 0 0 20 0 CTB 55 87 58 90 / 0 0 20 20 HLN 56 91 60 97 / 0 10 20 0 BZN 53 90 57 99 / 0 10 20 10 WYS 45 86 47 91 / 20 0 0 0 DLN 51 88 54 96 / 0 10 20 0 HVR 56 93 59 99 / 0 0 10 0 LWT 52 89 55 96 / 0 0 20 10

TFX WATCHES/WARNINGS/ADVISORIES

Heat Advisory from noon Saturday to 9 PM MDT Monday for Bears Paw Mountains and Southern Blaine-Canyon Ferry Area-Cascade County below 5000ft-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Fergus County below 4500ft-Gallatin Valley- Gates of the Mountains-Helena Valley-Hill County-Judith Basin County and Judith Gap-Madison River Valley-Missouri Headwaters- Northern Blaine County-Southern High Plains-Western and Central Chouteau County.