NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260513_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 05/13 00Z 0.09 2902  55  17   1 0.00
Wed 05/13 01Z 0.08 2702  55  20   1 0.00
Wed 05/13 02Z 0.08 2202  57  20   1 0.00
Wed 05/13 03Z 0.10 2004  59  15   1 0.00
Wed 05/13 04Z 0.11 2104  58  13   1 0.00
Wed 05/13 05Z 0.08 1906  57  12   2 0.00
Wed 05/13 06Z 0.12 1909  57  12   2 0.00
Wed 05/13 07Z 0.16 1911  56  24   2 0.00
Wed 05/13 08Z 0.21 2011  57  86   2 0.00
Wed 05/13 09Z 0.17 1910  59  93   1 0.00
Wed 05/13 10Z 0.09 1714  63  99   1 0.00
Wed 05/13 11Z 0.10 1719  74  99   1 0.00
Wed 05/13 12Z 0.15 1820  90  99   2 0.02
Wed 05/13 13Z 0.18 1920  96  98   3 0.03
Wed 05/13 14Z 0.22 2018  96  96   3 0.05
Wed 05/13 15Z 0.13 1817  94  97   3 0.06
Wed 05/13 16Z 0.08 1720  92  97   4 0.05
Wed 05/13 17Z 0.05 1722  85  90   5 0.03
Wed 05/13 18Z 0.13 1824  88  97   5 0.01
Wed 05/13 19Z 0.12 1825  89  96   5 0.02
Wed 05/13 20Z 0.19 1825  93  94   5 0.02
Wed 05/13 21Z 0.21 1825  96  96   5 0.04
Wed 05/13 22Z 0.22 1828  97  97   5 0.07
Wed 05/13 23Z 0.32 1930  97  93   6 0.06
Thu 05/14 00Z 0.35 1928  96  96   6 0.07
Thu 05/14 01Z 0.40 1931  94  86   6 0.06
Thu 05/14 02Z 0.49 2033  91  81   6 0.01
Thu 05/14 03Z 0.50 1934  84  72   6 0.01
Thu 05/14 04Z 0.51 2033  81  82   6 0.00
Thu 05/14 05Z 0.47 2030  88  92   6 0.03
Thu 05/14 06Z 0.42 1930  91  87   6 0.03
Thu 05/14 07Z 0.43 2029  96  85   5 0.02
Thu 05/14 08Z 0.42 2027  96  83   5 0.03
Thu 05/14 09Z 0.32 1922  97  73   5 0.02
Thu 05/14 10Z 0.25 1921  98  87   5 0.01
Thu 05/14 11Z 0.16 1818  98  88   5 0.02
Thu 05/14 12Z 0.07 1717  98  94   5 0.04
Thu 05/14 13Z 0.08 1619  98  98   5 0.09
Thu 05/14 14Z 0.16 1519  97  98   5 0.12
Thu 05/14 15Z 0.24 1419  97  98   5 0.12
Thu 05/14 16Z 0.35 1320  97  99   5 0.13
Thu 05/14 17Z 0.46 1220  97  98   5 0.13
Thu 05/14 18Z 0.54 1221  97  96   6 0.13
Thu 05/14 19Z 0.54 1121  98  97   6 0.08
Thu 05/14 20Z 0.59 1120  97  97   6 0.08
Thu 05/14 21Z 0.51 1117  97  98   6 0.06
Thu 05/14 22Z 0.55 0918  98  99   6 0.18
Thu 05/14 23Z 0.61 0921  99  95   6 0.14
Fri 05/15 00Z 0.62 0921  99  86   6 0.07
Fri 05/15 01Z 0.52 1019  98  78   6 0.06
Fri 05/15 02Z 0.39 1018  98  76   7 0.03
Fri 05/15 03Z 0.44 1020  97  78   7 0.02
Fri 05/15 04Z 0.44 1021  96  89   7 0.04
Fri 05/15 05Z 0.47 1022  94  93   7 0.07
Fri 05/15 06Z 0.52 1023  95  97   7 0.07
Fri 05/15 07Z 0.56 0924  95  98   6 0.11
Fri 05/15 08Z 0.66 0927  96  97   6 0.12
Fri 05/15 09Z 0.80 0931  96  94   5 0.09
Fri 05/15 10Z 0.77 0929  93  95   5 0.04
Fri 05/15 11Z 0.73 0826  93  96   4 0.02

Run total areal avg QPF for the Central_Greens is: 2.81 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