NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250602_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)
=== ===== === ==== ==== === === === ====
Mon 06/02 06Z 0.72 2617  95  45   0 0.00
Mon 06/02 07Z 0.70 2619  94  59   1 0.01
Mon 06/02 08Z 0.69 2720  96  71   1 0.02
Mon 06/02 09Z 0.65 2820  96  88   0 0.02
Mon 06/02 10Z 0.58 2918  94  92   0 0.01
Mon 06/02 11Z 0.50 2917  91  91   1 0.00
Mon 06/02 12Z 0.55 2918  91  77   1 0.00
Mon 06/02 13Z 0.62 2818  90  46   2 0.00
Mon 06/02 14Z 0.66 2818  83  18   2 0.00
Mon 06/02 15Z 1.07 2717  85   5   3 0.00
Mon 06/02 16Z 8.01 2616  84   1   3 0.00
Mon 06/02 17Z 9.94 2716  77   5   3 0.00
Mon 06/02 18Z 8.33 2715  74  10   4 0.00
Mon 06/02 19Z 8.36 2714  71  11   4 0.00
Mon 06/02 20Z 7.35 2713  71  10   4 0.00
Mon 06/02 21Z 5.62 2612  72  11   5 0.00
Mon 06/02 22Z 2.13 2611  72  16   5 0.00
Mon 06/02 23Z 0.94 2612  71  27   5 0.00
Tue 06/03 00Z 0.78 2713  68  22   5 0.00
Tue 06/03 01Z 0.82 2915  62  24   5 0.00
Tue 06/03 02Z 0.94 3015  62  24   5 0.00
Tue 06/03 03Z 0.87 3014  61  21   5 0.00
Tue 06/03 04Z 0.73 3013  60  18   5 0.00
Tue 06/03 05Z 0.54 3011  55  16   5 0.00
Tue 06/03 06Z 0.54 2910  53  13   5 0.00
Tue 06/03 07Z 0.52 2909  53  12   5 0.00
Tue 06/03 08Z 0.38 3008  52  10   6 0.00
Tue 06/03 09Z 0.27 3007  51   9   6 0.00
Tue 06/03 10Z 0.25 3007  49   9   6 0.00
Tue 06/03 11Z 0.16 3105  46  10   6 0.00
Tue 06/03 12Z 0.16 3104  45  11   6 0.00
Tue 06/03 13Z 0.30 2704  47   8   6 0.00
Tue 06/03 14Z 0.72 2605  51   4   7 0.00
Tue 06/03 15Z 1.44 2505  51   4   7 0.00
Tue 06/03 16Z 2.87 2506  50   6   7 0.00
Tue 06/03 17Z 3.36 2606  48  20   8 0.00
Tue 06/03 18Z 2.72 2606  45  46   9 0.00
Tue 06/03 19Z 1.93 2507  47  72   9 0.00
Tue 06/03 20Z 1.11 2607  52  88   9 0.00
Tue 06/03 21Z 0.46 2606  55  83  10 0.00
Tue 06/03 22Z 0.36 2506  59  71  10 0.00
Tue 06/03 23Z 0.30 2407  62  57  11 0.00
Wed 06/04 00Z 0.24 2307  64  44  12 0.00
Wed 06/04 01Z 0.25 2307  64  39  12 0.00
Wed 06/04 02Z 0.29 2309  63  37  12 0.00
Wed 06/04 03Z 0.30 2310  63  31  13 0.00
Wed 06/04 04Z 0.29 2310  62  30  13 0.00
Wed 06/04 05Z 0.26 2310  60  28  13 0.00
Wed 06/04 06Z 0.28 2310  59  24  13 0.00
Wed 06/04 07Z 0.31 2311  58  18  14 0.00
Wed 06/04 08Z 0.35 2312  58  17  14 0.00
Wed 06/04 09Z 0.42 2414  60  15  13 0.00
Wed 06/04 10Z 0.47 2415  58  17  13 0.00
Wed 06/04 11Z 0.53 2416  59  17  13 0.00
Wed 06/04 12Z 0.54 2416  60  17  13 0.00
Wed 06/04 13Z 0.47 2414  58  16  13 0.00
Wed 06/04 14Z 0.42 2312  56  15  14 0.00
Wed 06/04 15Z 0.38 2111  56  12  14 0.00
Wed 06/04 16Z 0.50 1910  58  14  14 0.00
Wed 06/04 17Z 0.73 1811  59  14  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.06 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