NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260513_0000
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)
=== ===== === ==== ==== === === === ====
Wed 05/13 00Z 0.18 3003  58  24   0 0.00
Wed 05/13 01Z 0.16 2903  57  23   0 0.00
Wed 05/13 02Z 0.14 2603  58  22   0 0.00
Wed 05/13 03Z 0.13 2303  59  19   0 0.00
Wed 05/13 04Z 0.13 2304  58  17   1 0.00
Wed 05/13 05Z 0.08 2005  57  15   1 0.00
Wed 05/13 06Z 0.09 1907  56  15   1 0.00
Wed 05/13 07Z 0.12 2009  55  22   1 0.00
Wed 05/13 08Z 0.15 2010  55  62   1 0.00
Wed 05/13 09Z 0.12 1910  58  78   1 0.00
Wed 05/13 10Z 0.05 1813  62  96   1 0.00
Wed 05/13 11Z 0.04 1717  70  99   1 0.00
Wed 05/13 12Z 0.06 1819  83  99   1 0.01
Wed 05/13 13Z 0.10 1820  90  98   2 0.02
Wed 05/13 14Z 0.14 1819  93  95   2 0.04
Wed 05/13 15Z 0.07 1818  94  97   3 0.05
Wed 05/13 16Z 0.06 1721  92  97   4 0.05
Wed 05/13 17Z 0.06 1723  88  93   5 0.04
Wed 05/13 18Z 0.05 1825  89  97   5 0.02
Wed 05/13 19Z 0.04 1827  89  96   5 0.03
Wed 05/13 20Z 0.08 1827  92  94   5 0.02
Wed 05/13 21Z 0.11 1828  95  95   5 0.03
Wed 05/13 22Z 0.13 1829  95  95   5 0.05
Wed 05/13 23Z 0.19 1931  96  92   6 0.06
Thu 05/14 00Z 0.23 1930  95  93   6 0.05
Thu 05/14 01Z 0.26 1930  94  88   6 0.04
Thu 05/14 02Z 0.30 1933  92  81   6 0.01
Thu 05/14 03Z 0.35 2034  88  73   6 0.01
Thu 05/14 04Z 0.37 2034  85  78   6 0.00
Thu 05/14 05Z 0.34 2031  90  87   6 0.02
Thu 05/14 06Z 0.29 2029  91  88   6 0.03
Thu 05/14 07Z 0.27 2028  95  86   5 0.02
Thu 05/14 08Z 0.29 2028  97  84   5 0.02
Thu 05/14 09Z 0.25 2024  97  75   5 0.01
Thu 05/14 10Z 0.19 1921  98  82   5 0.01
Thu 05/14 11Z 0.13 1918  98  85   5 0.02
Thu 05/14 12Z 0.09 1816  98  92   5 0.03
Thu 05/14 13Z 0.13 1617  98  93   5 0.06
Thu 05/14 14Z 0.21 1518  97  96   5 0.08
Thu 05/14 15Z 0.31 1419  97  98   5 0.10
Thu 05/14 16Z 0.42 1420  96  98   5 0.12
Thu 05/14 17Z 0.51 1320  94  98   5 0.10
Thu 05/14 18Z 0.59 1221  96  96   5 0.11
Thu 05/14 19Z 0.60 1220  97  97   5 0.07
Thu 05/14 20Z 0.65 1119  96  97   6 0.07
Thu 05/14 21Z 0.60 0917  97  99   6 0.07
Thu 05/14 22Z 0.64 0819  98  99   6 0.16
Thu 05/14 23Z 0.67 0921  98  96   6 0.14
Fri 05/15 00Z 0.74 0923  98  90   6 0.09
Fri 05/15 01Z 0.68 0923  96  84   6 0.06
Fri 05/15 02Z 0.62 1023  96  78   7 0.03
Fri 05/15 03Z 0.63 1025  95  79   7 0.03
Fri 05/15 04Z 0.63 1026  95  88   7 0.04
Fri 05/15 05Z 0.59 1124  94  94   7 0.08
Fri 05/15 06Z 0.57 1024  95  96   7 0.09
Fri 05/15 07Z 0.59 1024  94  96   6 0.09
Fri 05/15 08Z 0.68 0927  94  95   6 0.09
Fri 05/15 09Z 0.80 0930  92  91   5 0.06
Fri 05/15 10Z 0.75 0928  86  95   5 0.03
Fri 05/15 11Z 0.71 0926  90  97   5 0.01

Run total areal avg QPF for the greens is: 2.47 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