NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260215_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 02/15 18Z 0.22 0907  59  35  -9 0.00
Sun 02/15 19Z 0.22 1007  57  43  -8 0.00
Sun 02/15 20Z 0.18 1207  55  47  -7 0.00
Sun 02/15 21Z 0.15 1308  51  47  -7 0.00
Sun 02/15 22Z 0.13 1409  46  47  -6 0.00
Sun 02/15 23Z 0.14 1511  41  44  -6 0.00
Mon 02/16 00Z 0.13 1512  38  38  -6 0.00
Mon 02/16 01Z 0.13 1513  37  31  -5 0.00
Mon 02/16 04Z 0.07 1718  33  22  -6 0.00
Mon 02/16 05Z 0.05 1719  37  24  -6 0.00
Mon 02/16 06Z 0.05 1819  41  39  -7 0.00
Mon 02/16 07Z 0.06 1818  47  59  -7 0.00
Mon 02/16 08Z 0.06 1817  55  76  -6 0.00
Mon 02/16 09Z 0.05 1816  64  87  -6 0.00
Mon 02/16 10Z 0.04 1815  73  88  -5 0.00
Mon 02/16 11Z 0.03 1814  76  90  -5 0.00
Mon 02/16 12Z 0.03 1813  79  92  -5 0.00
Mon 02/16 13Z 0.04 1812  83  91  -5 0.00
Mon 02/16 14Z 0.04 1812  86  87  -5 0.00
Mon 02/16 15Z 0.04 1812  88  84  -5 0.00
Mon 02/16 16Z 0.05 1911  90  79  -5 0.00
Mon 02/16 17Z 0.04 1810  89  71  -4 0.00
Mon 02/16 18Z 0.05 1910  89  63  -4 0.00
Mon 02/16 19Z 0.06 1909  87  54  -4 0.00
Mon 02/16 20Z 0.11 2010  87  51  -4 0.00
Mon 02/16 21Z 0.12 2011  88  44  -4 0.00
Mon 02/16 22Z 0.07 1912  87  40  -4 0.00
Mon 02/16 23Z 0.13 2014  88  40  -5 0.00
Tue 02/17 00Z 0.17 2014  90  41  -5 0.00
Tue 02/17 01Z 0.20 2115  91  48  -4 0.00
Tue 02/17 02Z 0.22 2115  90  82  -4 0.00
Tue 02/17 03Z 0.23 2117  91  85  -4 0.00
Tue 02/17 04Z 0.22 2116  90  92  -3 0.00
Tue 02/17 05Z 0.24 2217  90  88  -3 0.00
Tue 02/17 06Z 0.26 2218  90  79  -3 0.00
Tue 02/17 07Z 0.28 2218  89  89  -3 0.00
Tue 02/17 08Z 0.26 2216  88  92  -2 0.00
Tue 02/17 09Z 0.26 2314  92  92  -3 0.00
Tue 02/17 10Z 0.27 2315  95  94  -3 0.00
Tue 02/17 11Z 0.29 2316  95  94  -3 0.00
Tue 02/17 12Z 0.29 2314  94  92  -3 0.01
Tue 02/17 13Z 0.29 2413  94  88  -3 0.01
Tue 02/17 14Z 0.30 2512  96  80  -3 0.01
Tue 02/17 15Z 0.29 2511  97  62  -4 0.00
Tue 02/17 16Z 0.30 2611  97  55  -4 0.01
Tue 02/17 17Z 0.32 2712  97  27  -3 0.01
Tue 02/17 18Z 0.38 2814  97  16  -3 0.01
Tue 02/17 19Z 0.40 2815  97  15  -3 0.00
Tue 02/17 20Z 0.48 2916  97  20  -4 0.00
Tue 02/17 21Z 0.55 2817  92  23  -4 0.01
Tue 02/17 22Z 0.52 2819  79  17  -3 0.01
Tue 02/17 23Z 0.48 2920  64  15  -2 0.01
Wed 02/18 00Z 0.48 2921  57  13  -2 0.01
Wed 02/18 01Z 0.52 2923  53  17  -3 0.01
Wed 02/18 02Z 0.52 2923  51  20  -3 0.01
Wed 02/18 03Z 0.55 2925  51  22  -4 0.00
Wed 02/18 04Z 0.53 2925  52  25  -4 0.00
Wed 02/18 05Z 0.52 3025  54  23  -5 0.00

Run total areal avg QPF for the greens is: 0.12 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