NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250917_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 09/17 06Z 0.16 1207  72  17  11 0.00
Wed 09/17 07Z 0.15 1207  70  18  11 0.00
Wed 09/17 08Z 0.17 1208  66  18  11 0.00
Wed 09/17 09Z 0.16 1208  61  17  11 0.00
Wed 09/17 10Z 0.15 1208  55  16  12 0.00
Wed 09/17 11Z 0.15 1209  48  16  12 0.00
Wed 09/17 12Z 0.11 1308  42  14  12 0.00
Wed 09/17 13Z 0.09 1407  38  14  13 0.00
Wed 09/17 14Z 0.08 1408  35  14  13 0.00
Wed 09/17 15Z 0.04 1507  35  19  13 0.00
Wed 09/17 16Z 0.02 1606  37  24  13 0.00
Wed 09/17 17Z 0.02 1704  41  26  13 0.00
Wed 09/17 18Z 0.03 1703  46  30  13 0.00
Wed 09/17 19Z 0.05 1703  51  32  12 0.00
Wed 09/17 20Z 0.07 1902  54  37  12 0.00
Wed 09/17 21Z 0.03 1802  55  32  12 0.00
Wed 09/17 22Z 0.03 1703  54  30  12 0.00
Wed 09/17 23Z 0.05 1804  51  32  13 0.00
Thu 09/18 00Z 0.07 1905  47  34  13 0.00
Thu 09/18 01Z 0.09 1906  45  36  13 0.00
Thu 09/18 02Z 0.11 2007  44  34  13 0.00
Thu 09/18 03Z 0.16 2108  45  37  14 0.00
Thu 09/18 04Z 0.19 2209  49  42  14 0.00
Thu 09/18 05Z 0.23 2310  49  45  13 0.00
Thu 09/18 06Z 0.26 2410  47  42  13 0.00
Thu 09/18 07Z 0.29 2411  48  39  13 0.00
Thu 09/18 08Z 0.27 2510  46  33  13 0.00
Thu 09/18 09Z 0.26 2510  48  30  13 0.00
Thu 09/18 10Z 0.26 2609  51  28  13 0.00
Thu 09/18 11Z 0.22 2708  51  26  12 0.00
Thu 09/18 12Z 0.20 2707  53  19  12 0.00
Thu 09/18 13Z 0.19 2707  55  11  12 0.00
Thu 09/18 14Z 0.17 2705  55  11  12 0.00
Thu 09/18 15Z 0.20 2606  57  18  12 0.00
Thu 09/18 16Z 0.26 2606  56  23  12 0.00
Thu 09/18 17Z 0.39 2607  53  25  12 0.00
Thu 09/18 18Z 0.48 2608  51  37  13 0.00
Thu 09/18 19Z 0.51 2708  55  45  13 0.00
Thu 09/18 20Z 0.74 2709  60  61  12 0.00
Thu 09/18 21Z 1.13 2712  66  62  12 0.00
Thu 09/18 22Z 1.02 2715  73  52  12 0.00
Thu 09/18 23Z 0.86 2816  83  45  12 0.00
Fri 09/19 00Z 0.71 2918  91  40  11 0.01
Fri 09/19 01Z 0.67 2918  91  51  11 0.00
Fri 09/19 02Z 0.55 3019  94  61  11 0.01
Fri 09/19 03Z 0.42 3120  95  59  11 0.01
Fri 09/19 04Z 0.28 3220  95  53  10 0.01
Fri 09/19 05Z 0.26 3220  96  51  10 0.01
Fri 09/19 06Z 0.27 3219  97  47   9 0.01
Fri 09/19 07Z 0.30 3220  96  45   8 0.01
Fri 09/19 08Z 0.27 3220  96  41   8 0.01
Fri 09/19 09Z 0.22 3220  94  31   8 0.00
Fri 09/19 10Z 0.19 3220  88  23   8 0.00
Fri 09/19 11Z 0.16 3220  76  35   8 0.00
Fri 09/19 12Z 0.12 3321  66  36   7 0.00
Fri 09/19 13Z 0.09 3320  56  29   7 0.00
Fri 09/19 14Z 0.08 3319  51  14   7 0.00
Fri 09/19 15Z 0.09 3318  48  11   7 0.00
Fri 09/19 16Z 0.09 3317  44   7   6 0.00
Fri 09/19 17Z 0.09 3317  40   3   6 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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