NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250905_1800
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 09/05 18Z 0.35 1912  87   6  11 0.00
Fri 09/05 19Z 0.46 1915  87   5  11 0.00
Fri 09/05 20Z 0.13 1919  84   7  12 0.00
Fri 09/05 21Z 0.13 2023  80  12  12 0.00
Fri 09/05 22Z 0.08 2024  81  18  12 0.00
Fri 09/05 23Z 0.13 2028  85  24  12 0.00
Sat 09/06 00Z 0.20 2034  85  39  12 0.00
Sat 09/06 01Z 0.29 2135  82  41  13 0.00
Sat 09/06 02Z 0.31 2136  87   1  13 0.00
Sat 09/06 03Z 0.35 2138  85  13  13 0.00
Sat 09/06 04Z 0.41 2141  87  40  14 0.00
Sat 09/06 05Z 0.54 2240  96  94  12 0.04
Sat 09/06 06Z 0.94 2626  96  67  10 0.14
Sat 09/06 07Z 0.73 2621  94  74  10 0.02
Sat 09/06 08Z 0.67 2620  92  67   9 0.01
Sat 09/06 09Z 0.58 2521  75  59  10 0.01
Sat 09/06 10Z 0.60 2520  74  71   9 0.00
Sat 09/06 11Z 0.54 2521  74  61  10 0.00
Sat 09/06 12Z 0.44 2421  76  59  10 0.00
Sat 09/06 13Z 0.37 2319  79  74  10 0.00
Sat 09/06 14Z 0.38 2318  80  82  10 0.00
Sat 09/06 15Z 0.35 2317  76  85   9 0.00
Sat 09/06 16Z 0.39 2415  69  95   9 0.00
Sat 09/06 17Z 0.56 2515  63  93   8 0.00
Sat 09/06 18Z 0.93 2716  82  97   7 0.01
Sat 09/06 19Z 0.73 2815  94  90   7 0.01
Sat 09/06 20Z 0.32 2613  94  94   7 0.03
Sat 09/06 21Z 0.32 2416  91  98   7 0.05
Sat 09/06 22Z 0.31 2418  81  96   9 0.03
Sat 09/06 23Z 0.32 2514  63  91   8 0.00
Sun 09/07 00Z 0.44 2715  51  88   8 0.00
Sun 09/07 01Z 0.49 2716  48  96   8 0.00
Sun 09/07 02Z 0.39 2613  60  92   7 0.00
Sun 09/07 03Z 0.39 2612  63  91   6 0.01
Sun 09/07 04Z 0.31 2609  67  92   6 0.01
Sun 09/07 05Z 0.31 2709  74  97   6 0.00
Sun 09/07 06Z 0.31 2708  82  97   5 0.00
Sun 09/07 07Z 0.29 2709  84  91   6 0.01
Sun 09/07 08Z 0.30 2709  86  86   6 0.00
Sun 09/07 09Z 0.26 2608  84  72   6 0.00
Sun 09/07 10Z 0.17 2506  80  72   6 0.00
Sun 09/07 11Z 0.12 2505  76  46   6 0.00
Sun 09/07 12Z 0.07 2403  74  20   6 0.00
Sun 09/07 13Z 0.07 2304  77  13   6 0.00
Sun 09/07 14Z 0.10 2304  80  12   5 0.00
Sun 09/07 15Z 0.16 2305  85  20   5 0.00
Sun 09/07 16Z 0.33 2306  88  26   5 0.00
Sun 09/07 17Z 0.82 2407  88  23   5 0.00
Sun 09/07 18Z 1.45 2409  87  28   5 0.00
Sun 09/07 19Z 1.32 2410  87  41   6 0.00
Sun 09/07 20Z 1.22 2511  85  64   6 0.01
Sun 09/07 21Z 1.49 2513  85  60   6 0.00
Sun 09/07 22Z 0.97 2514  89  66   6 0.00
Sun 09/07 23Z 0.76 2615  89  78   6 0.01
Mon 09/08 00Z 0.91 2618  87  64   5 0.00
Mon 09/08 01Z 0.96 2720  93  62   5 0.04
Mon 09/08 02Z 0.93 2823  92  68   4 0.04
Mon 09/08 03Z 0.99 2923  90  44   4 0.02
Mon 09/08 04Z 0.75 2922  78  29   4 0.01
Mon 09/08 05Z 0.84 2922  81  34   3 0.00

Run total areal avg QPF for the Northern_Greens is: 0.51 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