National Weather Service United States Department of Commerce

Severe Weather and Flooding Threats for the Central U.S.; Dangerous Heat in the Southern and Western U.S.

Severe weather and flooding threats will continue for portions of the central U.S. over the next couple of days, with multiple rounds of thunderstorms expected. Dangerous heat will persist across the southern and western U.S. through mid-week. Hot and dry conditions will fuel fire weather concerns for the Intermountain West, where dry thunderstorms may spark additional wildfires. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260624_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 06/24 06Z 0.18 3317  79  71   9 0.00
Wed 06/24 07Z 0.21 3316  79  52   9 0.00
Wed 06/24 08Z 0.27 3218  82  40   9 0.00
Wed 06/24 09Z 0.31 3220  83  39   9 0.00
Wed 06/24 10Z 0.30 3220  82  35   9 0.00
Wed 06/24 11Z 0.32 3220  83  34   9 0.00
Wed 06/24 12Z 0.34 3120  86  34   8 0.00
Wed 06/24 13Z 0.39 3120  86  39   8 0.00
Wed 06/24 14Z 0.46 3119  86  43   8 0.00
Wed 06/24 15Z 0.68 3117  87  46   8 0.00
Wed 06/24 16Z 1.97 3017  92  49   8 0.00
Wed 06/24 17Z 1.84 2917  90  44   8 0.00
Wed 06/24 18Z 3.64 2915  86  44   8 0.00
Wed 06/24 19Z 6.86 2916  83  44   9 0.00
Wed 06/24 20Z 7.73 2915  81  41   9 0.00
Wed 06/24 21Z 7.61 2918  76  46   9 0.00
Wed 06/24 22Z 4.64 2918  73  45  10 0.00
Wed 06/24 23Z 2.79 2920  73  46  10 0.00
Thu 06/25 00Z 2.01 2920  73  45   9 0.00
Thu 06/25 01Z 1.42 2921  80  44   9 0.00
Thu 06/25 02Z 0.85 2921  81  38   9 0.00
Thu 06/25 03Z 0.76 3020  78  30   9 0.00
Thu 06/25 04Z 0.69 3021  77  28   9 0.00
Thu 06/25 05Z 0.57 3019  74  22   9 0.00
Thu 06/25 06Z 0.51 3018  73  22   9 0.00
Thu 06/25 07Z 0.43 3116  70  13  10 0.00
Thu 06/25 08Z 0.42 3114  70   9  10 0.00
Thu 06/25 09Z 0.41 3011  70  12   9 0.00
Thu 06/25 10Z 0.40 2909  69  16   9 0.00
Thu 06/25 11Z 0.37 2707  69  14   9 0.00
Thu 06/25 12Z 0.32 2606  70  13   9 0.00
Thu 06/25 13Z 0.35 2506  73  21   9 0.00
Thu 06/25 14Z 0.59 2406  76  21   9 0.00
Thu 06/25 15Z 1.35 2406  77  19   9 0.00
Thu 06/25 16Z 2.07 2406  76  28   9 0.00
Thu 06/25 17Z 1.73 2307  75  40  10 0.00
Thu 06/25 18Z 2.31 2209  73  56  10 0.00
Thu 06/25 19Z 2.22 2211  69  64  10 0.00
Thu 06/25 20Z 0.62 2211  63  65  10 0.00
Thu 06/25 21Z 0.38 2309  54  61  10 0.00
Thu 06/25 22Z 0.25 2108  49  62  11 0.00
Thu 06/25 23Z 0.26 2008  52  81  11 0.00
Fri 06/26 00Z 0.17 1808  63  96  10 0.00
Fri 06/26 01Z 0.05 1612  72  97  10 0.00
Fri 06/26 02Z 0.05 1617  81  99  10 0.01
Fri 06/26 03Z 0.11 1720  91  98  10 0.05
Fri 06/26 04Z 0.19 1825  95  94  11 0.19
Fri 06/26 05Z 0.46 2026  95  91  11 0.11
Fri 06/26 06Z 0.50 2028  97  95  11 0.13
Fri 06/26 07Z 0.78 2232  96  87  11 0.21
Fri 06/26 08Z 0.74 2228  90  86  11 0.02
Fri 06/26 09Z 0.77 2328  94  82  11 0.04
Fri 06/26 10Z 0.65 2424  95  50  11 0.02
Fri 06/26 11Z 0.61 2422  93  37  11 0.02
Fri 06/26 12Z 0.56 2420  90  31  11 0.01
Fri 06/26 13Z 0.52 2518  88  32  12 0.01
Fri 06/26 14Z 0.51 2517  88  50  12 0.00
Fri 06/26 15Z 0.50 2415  86  59  12 0.00
Fri 06/26 16Z 0.55 2415  84  68  12 0.00
Fri 06/26 17Z 0.73 2315  85  56  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.82 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1