NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260819_1200
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 08/19 12Z 0.20 2405  85  24  11 0.00
Wed 08/19 13Z 0.23 2306  83  27  12 0.00
Wed 08/19 14Z 0.30 2207  81  32  12 0.00
Wed 08/19 15Z 0.54 2308  76  40  12 0.00
Wed 08/19 16Z 1.19 2409  71  46  12 0.00
Wed 08/19 17Z 1.22 2411  68  59  12 0.00
Wed 08/19 18Z 1.25 2513  67  69  13 0.00
Wed 08/19 19Z 0.99 2415  70  77  13 0.00
Wed 08/19 20Z 1.12 2518  82  89  12 0.00
Wed 08/19 21Z 1.17 2516  84  85  13 0.00
Wed 08/19 22Z 1.37 2516  89  87  13 0.01
Wed 08/19 23Z 0.82 2516  89  79  12 0.02
Thu 08/20 00Z 0.90 2618  87  67  13 0.00
Thu 08/20 01Z 0.82 2618  87  45  12 0.00
Thu 08/20 02Z 0.62 2616  85  23  13 0.00
Thu 08/20 03Z 0.52 2616  83  21  13 0.00
Thu 08/20 04Z 0.44 2715  75  28  13 0.00
Thu 08/20 05Z 0.41 2815  73  37  13 0.00
Thu 08/20 06Z 0.38 2916  73  31  13 0.00
Thu 08/20 07Z 0.37 2916  74  24  12 0.00
Thu 08/20 08Z 0.28 3014  76  25  12 0.00
Thu 08/20 09Z 0.25 3113  75  33  12 0.00
Thu 08/20 10Z 0.23 3112  74  16  11 0.00
Thu 08/20 11Z 0.23 3111  74  12  11 0.00
Thu 08/20 12Z 0.22 3110  73  13  10 0.00
Thu 08/20 13Z 0.19 3109  70  12  10 0.00
Thu 08/20 14Z 0.22 3007  70  13  10 0.00
Thu 08/20 16Z 0.51 3003  69   9  10 0.00
Thu 08/20 17Z 1.04 2804  63  19  10 0.00
Thu 08/20 18Z 0.65 2903  58   9  11 0.00
Thu 08/20 19Z 0.84 2804  58  11  11 0.00
Thu 08/20 20Z 0.58 2805  58  19  11 0.00
Thu 08/20 21Z 0.33 2704  61  14  11 0.00
Thu 08/20 22Z 0.30 2705  66  10  11 0.00
Thu 08/20 23Z 0.25 2804  71  12  11 0.00
Fri 08/21 00Z 0.23 2804  75  12  11 0.00
Fri 08/21 01Z 0.20 2904  78  14  10 0.00
Fri 08/21 02Z 0.19 2803  80  18  10 0.00
Fri 08/21 03Z 0.14 2802  82  16  10 0.00
Fri 08/21 04Z 0.12 2902  84  17  10 0.00
Fri 08/21 05Z 0.10 2902  84  18  10 0.00
Fri 08/21 06Z 0.06 2801  85  18  10 0.00
Fri 08/21 07Z 0.06 2501  85  18   9 0.00
Fri 08/21 08Z 0.06 1800  85  18   9 0.00
Fri 08/21 10Z 0.08 1501  86  19   9 0.00
Fri 08/21 11Z 0.10 1302  87  19   9 0.00
Fri 08/21 13Z 0.14 1407  88  21   9 0.00
Fri 08/21 14Z 0.17 1409  87  21   9 0.00
Fri 08/21 15Z 0.17 1408  86  22   9 0.00
Fri 08/21 16Z 0.49 1407  85  22   9 0.00
Fri 08/21 17Z 0.98 1407  84  24   9 0.00
Fri 08/21 18Z 0.83 1406  85  27  10 0.00
Fri 08/21 20Z 0.12 1505  88  30  10 0.00
Fri 08/21 21Z 0.08 1504  90  34  10 0.00
Fri 08/21 22Z 0.11 1405  90  39  11 0.00
Fri 08/21 23Z 0.08 1406  90  42  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.03 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