NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260909_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 09/09 12Z 0.31 2016  81  62  11 0.00
Wed 09/09 13Z 0.36 2019  79  61  12 0.00
Wed 09/09 14Z 0.36 2019  79  55  12 0.00
Wed 09/09 15Z 0.39 2119  79  46  12 0.00
Wed 09/09 16Z 0.42 2118  82  31  12 0.00
Wed 09/09 17Z 0.40 2019  91  25  13 0.00
Wed 09/09 18Z 0.39 2020  94  41  13 0.01
Wed 09/09 19Z 0.38 2021  93  25  13 0.02
Wed 09/09 20Z 0.38 1922  92  56  13 0.01
Wed 09/09 21Z 0.60 2026  96  88  13 0.01
Wed 09/09 22Z 0.64 2126  96  97  13 0.06
Wed 09/09 23Z 0.72 2129  97  98  13 0.12
Thu 09/10 00Z 0.87 2233  96  98  14 0.10
Thu 09/10 01Z 0.95 2234  96  95  14 0.13
Thu 09/10 02Z 0.87 2236  98  97  16 0.07
Thu 09/10 03Z 1.04 2243  98  93  16 0.22
Thu 09/10 04Z 1.08 2243  97  90  16 0.15
Thu 09/10 05Z 1.13 2342  97  89  16 0.06
Thu 09/10 06Z 1.14 2343  97  91  16 0.13
Thu 09/10 07Z 1.12 2441  98  89  16 0.18
Thu 09/10 08Z 1.11 2536  97  91  15 0.24
Thu 09/10 09Z 0.95 2629  94  87  15 0.19
Thu 09/10 10Z 0.92 2727  94  56  14 0.09
Thu 09/10 11Z 0.88 2726  89  25  14 0.02
Thu 09/10 12Z 0.97 2728  84  25  13 0.01
Thu 09/10 13Z 0.94 2731  71  15  13 0.00
Thu 09/10 14Z 0.99 2730  67   6  13 0.00
Thu 09/10 15Z 1.41 2728  66   5  12 0.00
Thu 09/10 16Z 2.97 2728  63   8  11 0.00
Thu 09/10 17Z 8.89 2727  61  10  11 0.00
Thu 09/10 18Z 16.75 2727  62  10  10 0.00
Thu 09/10 19Z 18.69 2728  60  10  11 0.00
Thu 09/10 20Z 18.09 2728  59  10  11 0.00
Thu 09/10 21Z 11.39 2826  63   9  10 0.00
Thu 09/10 22Z 3.81 2825  73  12  10 0.00
Thu 09/10 23Z 1.96 2925  84   7   9 0.01
Fri 09/11 00Z 1.19 2927  93   8   8 0.01
Fri 09/11 01Z 0.79 3026  96   6   7 0.01
Fri 09/11 02Z 0.73 3026  95   5   6 0.01
Fri 09/11 03Z 0.66 3026  93   5   5 0.01
Fri 09/11 04Z 0.65 3026  91   4   4 0.01
Fri 09/11 05Z 0.61 3025  89   4   4 0.00
Fri 09/11 06Z 0.55 3026  86   2   4 0.00
Fri 09/11 07Z 0.45 3024  85   2   4 0.00
Fri 09/11 08Z 0.40 3124  83   5   5 0.00
Fri 09/11 09Z 0.36 3124  79   4   5 0.00
Fri 09/11 10Z 0.34 3123  74   3   5 0.00
Fri 09/11 11Z 0.34 3023  73   2   6 0.00
Fri 09/11 12Z 0.36 3024  73   2   5 0.00
Fri 09/11 13Z 0.35 3024  68   3   6 0.00
Fri 09/11 14Z 0.34 3124  61   4   6 0.00
Fri 09/11 15Z 0.34 3123  57   4   6 0.00
Fri 09/11 16Z 0.39 3123  56   4   6 0.00
Fri 09/11 17Z 0.46 3022  57   5   6 0.00
Fri 09/11 18Z 0.62 3020  62   5   6 0.00
Fri 09/11 19Z 1.20 2918  63   5   6 0.00
Fri 09/11 20Z 1.64 2918  59   7   6 0.00
Fri 09/11 21Z 1.14 3017  55   9   6 0.00
Fri 09/11 22Z 0.87 2918  54  13   7 0.00
Fri 09/11 23Z 0.79 3019  54  18   7 0.00

Run total areal avg QPF for the Central_Greens is: 1.88 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