NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260225_0000
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 02/25 00Z 0.61 2714  81  17 -15 0.00
Wed 02/25 01Z 0.50 2713  80  11 -15 0.00
Wed 02/25 02Z 0.49 2716  78   8 -14 0.00
Wed 02/25 03Z 0.39 2614  73  11 -14 0.00
Wed 02/25 04Z 0.28 2412  65  31 -12 0.00
Wed 02/25 05Z 0.33 2316  65  49 -13 0.00
Wed 02/25 06Z 0.32 2217  57  55 -12 0.00
Wed 02/25 08Z 0.43 2320  62  85 -12 0.00
Wed 02/25 09Z 0.35 2119  67  59 -11 0.00
Wed 02/25 10Z 0.28 2022  68  74 -10 0.00
Wed 02/25 11Z 0.31 2027  76  93 -10 0.00
Wed 02/25 12Z 0.30 1929  91  87  -9 0.00
Wed 02/25 13Z 0.32 1930  92  87  -9 0.01
Wed 02/25 14Z 0.39 2028  93  86  -9 0.04
Wed 02/25 16Z 0.46 2119  95  86  -8 0.04
Wed 02/25 17Z 0.52 2116  96  59  -8 0.03
Wed 02/25 18Z 0.68 2115  95  42  -8 0.02
Wed 02/25 19Z 1.04 2115  94  54  -8 0.01
Wed 02/25 20Z 1.03 2116  94  73  -7 0.00
Wed 02/25 21Z 0.92 2217  95  80  -7 0.00
Wed 02/25 22Z 0.91 2219  96  83  -7 0.01
Thu 02/26 00Z 0.72 2223  95  81  -6 0.00
Thu 02/26 01Z 0.83 2228  96  82  -5 0.01
Thu 02/26 02Z 1.07 2328  96  91  -5 0.00
Thu 02/26 03Z 1.61 2425  92  87  -7 0.00
Thu 02/26 04Z 1.77 2525  89  86  -8 0.01
Thu 02/26 05Z 1.36 2523  90  71  -9 0.03
Thu 02/26 06Z 1.06 2622  90  76  -9 0.03
Thu 02/26 07Z 1.03 2523  94  29 -10 0.01
Thu 02/26 08Z 1.33 2625  95  27 -11 0.00
Thu 02/26 09Z 1.86 2726  93  29 -12 0.00
Thu 02/26 10Z 2.23 2726  88  29 -14 0.00
Thu 02/26 11Z 1.32 2727  76  27 -14 0.01
Thu 02/26 12Z 1.17 2729  68  16 -14 0.01
Thu 02/26 13Z 1.34 2729  68   8 -14 0.00
Thu 02/26 14Z 1.68 2727  68   4 -15 0.00
Thu 02/26 15Z 5.15 2725  68   4 -15 0.00
Thu 02/26 16Z 10.83 2721  71   4 -15 0.00
Thu 02/26 17Z 11.20 2718  74   5 -15 0.00
Thu 02/26 18Z 11.14 2617  75   6 -14 0.00
Thu 02/26 19Z 11.80 2618  77   7 -14 0.00
Thu 02/26 20Z 11.37 2619  76   9 -14 0.00
Thu 02/26 21Z 8.66 2619  75  12 -13 0.00
Thu 02/26 22Z 3.47 2621  76  16 -13 0.00
Thu 02/26 23Z 2.05 2722  73  20 -13 0.00
Fri 02/27 00Z 1.32 2822  71  24 -14 0.00
Fri 02/27 01Z 0.83 2821  71  27 -13 0.00
Fri 02/27 02Z 0.59 2821  66  33 -12 0.00
Fri 02/27 03Z 0.50 2820  63  36 -12 0.00
Fri 02/27 04Z 0.43 2820  59  45 -11 0.00
Fri 02/27 06Z 0.33 2817  50  59 -10 0.00
Fri 02/27 07Z 0.29 2815  46  46  -9 0.00
Fri 02/27 08Z 0.27 2815  41  50  -9 0.00
Fri 02/27 09Z 0.24 2814  38  54  -8 0.00
Fri 02/27 10Z 0.29 2615  39  62  -8 0.00
Fri 02/27 11Z 0.30 2615  39  74  -7 0.00

Run total areal avg QPF for the Central_Greens is: 0.27 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