NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260215_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)
=== ===== === ==== ==== === === === ====
Sun 02/15 00Z 0.78 2818  87  15 -10 0.00
Sun 02/15 01Z 0.90 2822  86  14 -10 0.00
Sun 02/15 02Z 0.91 2824  86  13 -10 0.00
Sun 02/15 03Z 0.87 2925  88  14 -10 0.00
Sun 02/15 04Z 0.94 2928  92  17 -10 0.00
Sun 02/15 05Z 0.78 3028  87  18 -10 0.00
Sun 02/15 06Z 0.66 3026  87  19 -10 0.00
Sun 02/15 07Z 0.58 3026  87  20 -10 0.00
Sun 02/15 08Z 0.50 3025  84  19 -11 0.01
Sun 02/15 09Z 0.39 3024  77  17 -10 0.00
Sun 02/15 10Z 0.27 3123  67  16  -9 0.00
Sun 02/15 11Z 0.17 3223  54  14  -9 0.00
Sun 02/15 12Z 0.09 3322  41  14  -9 0.00
Sun 02/15 13Z 0.04 3418  32  14  -8 0.00
Sun 02/15 14Z 0.04 3513  27  15  -8 0.00
Sun 02/15 15Z 0.05 0010  25  19  -7 0.00
Sun 02/15 16Z 0.07 0206  26  23  -7 0.00
Sun 02/15 17Z 0.07 0404  27  31  -7 0.00
Sun 02/15 18Z 0.07 0703  28  40  -7 0.00
Sun 02/15 19Z 0.04 1302  29  44  -6 0.00
Sun 02/15 20Z 0.03 1503  29  45  -6 0.00
Sun 02/15 21Z 0.02 1604  27  38  -5 0.00
Sun 02/15 22Z 0.02 1606  23  24  -4 0.00
Sun 02/15 23Z 0.03 1809  24  16  -4 0.00
Mon 02/16 00Z 0.04 1811  25  17  -4 0.00
Mon 02/16 01Z 0.09 1912  30  31  -5 0.00
Mon 02/16 02Z 0.10 1912  38  49  -4 0.00
Mon 02/16 03Z 0.12 1913  47  61  -4 0.00
Mon 02/16 04Z 0.14 1914  61  77  -5 0.00
Mon 02/16 05Z 0.14 1914  79  75  -5 0.00
Mon 02/16 06Z 0.11 1914  90  86  -5 0.01
Mon 02/16 07Z 0.11 1915  91  88  -5 0.01
Mon 02/16 08Z 0.12 1915  93  86  -4 0.02
Mon 02/16 09Z 0.12 1915  95  90  -4 0.02
Mon 02/16 10Z 0.15 1914  95  91  -5 0.02
Mon 02/16 11Z 0.15 2013  96  89  -5 0.02
Mon 02/16 12Z 0.16 2112  97  82  -4 0.01
Mon 02/16 13Z 0.14 2111  96  75  -4 0.01
Mon 02/16 14Z 0.14 2111  96  70  -4 0.01
Mon 02/16 15Z 0.14 2110  97  62  -4 0.01
Mon 02/16 16Z 0.13 2109  97  56  -4 0.00
Mon 02/16 17Z 0.15 2110  97  49  -4 0.00
Mon 02/16 18Z 0.16 2110  97  48  -4 0.00
Mon 02/16 19Z 0.19 2111  97  42  -4 0.00
Mon 02/16 20Z 0.25 2212  97  33  -5 0.00
Mon 02/16 21Z 0.28 2212  97  42  -5 0.00
Mon 02/16 22Z 0.30 2213  97  42  -5 0.00
Mon 02/16 23Z 0.34 2314  96  80  -4 0.00
Tue 02/17 00Z 0.33 2315  93  84  -3 0.00
Tue 02/17 01Z 0.39 2417  92  81  -3 0.00
Tue 02/17 02Z 0.42 2418  90  91  -3 0.01
Tue 02/17 03Z 0.41 2517  92  90  -3 0.01
Tue 02/17 04Z 0.41 2617  95  89  -2 0.02
Tue 02/17 05Z 0.42 2717  86  89  -2 0.01
Tue 02/17 06Z 0.42 2617  80  88  -3 0.00
Tue 02/17 07Z 0.42 2717  83  91  -3 0.01
Tue 02/17 08Z 0.39 2716  88  86  -3 0.01
Tue 02/17 09Z 0.34 2815  90  84  -2 0.00
Tue 02/17 10Z 0.31 2813  87  82  -2 0.00
Tue 02/17 11Z 0.30 2812  89  74  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.22 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