NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250205_0000
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)
=== ===== === ==== ==== === === === ====
Wed 02/05 00Z 5.07 3030  87  38 -19 0.00
Wed 02/05 01Z 4.59 3033  86  37 -20 0.00
Wed 02/05 02Z 3.37 3132  82  37 -20 0.00
Wed 02/05 03Z 1.83 3132  80  31 -20 0.00
Wed 02/05 04Z 1.32 3132  77  18 -19 0.00
Wed 02/05 05Z 0.90 3131  77  19 -19 0.00
Wed 02/05 06Z 0.75 3031  73  23 -18 0.00
Wed 02/05 07Z 0.67 3030  73  19 -18 0.00
Wed 02/05 08Z 0.61 3029  74  19 -18 0.00
Wed 02/05 09Z 0.56 3026  78  21 -19 0.00
Wed 02/05 10Z 0.49 3025  78  22 -19 0.00
Wed 02/05 11Z 0.42 3023  75  17 -18 0.00
Wed 02/05 12Z 0.40 3022  73  15 -18 0.00
Wed 02/05 13Z 0.39 3022  72  13 -18 0.00
Wed 02/05 14Z 0.39 3021  71  14 -18 0.00
Wed 02/05 15Z 0.40 2921  71  18 -18 0.00
Wed 02/05 16Z 0.42 2921  72  17 -18 0.00
Wed 02/05 17Z 0.44 2921  75  18 -18 0.00
Wed 02/05 18Z 0.45 2920  76  14 -18 0.00
Wed 02/05 19Z 0.45 2920  72  12 -17 0.00
Wed 02/05 20Z 0.42 2819  67   9 -16 0.00
Wed 02/05 21Z 0.45 2820  62  10 -16 0.00
Wed 02/05 22Z 0.45 2820  54  13 -15 0.00
Wed 02/05 23Z 0.46 2821  50  18 -14 0.00
Thu 02/06 00Z 0.44 2820  46  18 -14 0.00
Thu 02/06 01Z 0.39 2819  41  20 -13 0.00
Thu 02/06 02Z 0.33 2816  36  19 -12 0.00
Thu 02/06 03Z 0.27 2814  30  17 -11 0.00
Thu 02/06 04Z 0.24 2713  28  15 -11 0.00
Thu 02/06 05Z 0.21 2612  26  13 -11 0.00
Thu 02/06 06Z 0.19 2512  23  14 -11 0.00
Thu 02/06 07Z 0.14 2312  19  13 -10 0.00
Thu 02/06 08Z 0.09 2211  16  13  -9 0.00
Thu 02/06 09Z 0.06 2113  16  11  -9 0.00
Thu 02/06 10Z 0.03 1915  15  11  -8 0.00
Thu 02/06 11Z 0.03 1918  17  17  -8 0.00
Thu 02/06 12Z 0.07 1922  20  32  -8 0.00
Thu 02/06 13Z 0.07 1927  28  48  -8 0.00
Thu 02/06 14Z 0.09 1928  37  89  -7 0.00
Thu 02/06 15Z 0.12 1831  61  97  -8 0.00
Thu 02/06 16Z 0.15 1832  87  97  -8 0.02
Thu 02/06 17Z 0.12 1836  92  98  -7 0.05
Thu 02/06 18Z 0.10 1939  94  98  -7 0.05
Thu 02/06 19Z 0.10 1938  96  97  -7 0.05
Thu 02/06 20Z 0.07 1937  96  85  -6 0.04
Thu 02/06 21Z 0.04 1936  96  74  -5 0.03
Thu 02/06 22Z 0.04 2033  96  60  -4 0.02
Thu 02/06 23Z 0.10 2032  97  20  -4 0.01
Fri 02/07 00Z 0.12 2130  96  28  -3 0.01
Fri 02/07 01Z 0.22 2130  96  37  -4 0.01
Fri 02/07 02Z 0.38 2231  96  27  -5 0.01
Fri 02/07 03Z 0.60 2331  98   7  -6 0.01
Fri 02/07 04Z 0.84 2431  97   3  -6 0.02
Fri 02/07 05Z 1.33 2432  98   7  -7 0.02
Fri 02/07 06Z 1.67 2532  98  14  -8 0.02
Fri 02/07 07Z 1.60 2534  97  24  -9 0.01
Fri 02/07 08Z 2.39 2634  96  61  -9 0.03
Fri 02/07 09Z 1.76 2634  92  70 -10 0.01
Fri 02/07 10Z 3.17 2634  90  84 -11 0.01
Fri 02/07 11Z 3.58 2735  87  93 -13 0.02

Run total areal avg QPF for the Northern_Greens is: 0.45 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