NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260429_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 04/29 00Z 0.16 1514  58  45   7 0.00
Wed 04/29 01Z 0.09 1618  63  29   6 0.00
Wed 04/29 02Z 0.04 1618  61  34   6 0.00
Wed 04/29 03Z 0.05 1718  57  50   5 0.00
Wed 04/29 04Z 0.08 1718  56  67   5 0.00
Wed 04/29 05Z 0.18 1819  57  82   5 0.00
Wed 04/29 06Z 0.35 2021  57  92   4 0.00
Wed 04/29 07Z 0.36 2020  63  90   4 0.00
Wed 04/29 08Z 0.26 2016  62  70   4 0.00
Wed 04/29 09Z 0.26 2015  63  59   4 0.00
Wed 04/29 10Z 0.32 2117  67  52   4 0.00
Wed 04/29 11Z 0.26 2115  70  39   5 0.00
Wed 04/29 12Z 0.24 2114  74  38   5 0.00
Wed 04/29 13Z 0.18 2111  76  32   6 0.00
Wed 04/29 14Z 0.13 2008  77  24   6 0.00
Wed 04/29 15Z 0.07 1808  76  16   6 0.00
Wed 04/29 16Z 0.18 1608  74  12   6 0.00
Wed 04/29 17Z 0.31 1609  73  15   6 0.00
Wed 04/29 18Z 0.85 1509  73  20   6 0.00
Wed 04/29 19Z 1.58 1511  74  26   6 0.00
Wed 04/29 20Z 1.51 1513  75  41   6 0.00
Wed 04/29 21Z 1.37 1515  77  48   6 0.00
Wed 04/29 22Z 0.79 1516  80  60   6 0.00
Wed 04/29 23Z 0.51 1519  82  74   5 0.00
Thu 04/30 00Z 0.18 1621  85  75   5 0.00
Thu 04/30 01Z 0.11 1621  89  61   6 0.00
Thu 04/30 02Z 0.05 1621  87  63   6 0.00
Thu 04/30 03Z 0.05 1623  83  71   7 0.00
Thu 04/30 04Z 0.07 1625  78  64   7 0.00
Thu 04/30 05Z 0.09 1625  74  61   7 0.01
Thu 04/30 06Z 0.05 1725  73  81   6 0.01
Thu 04/30 07Z 0.10 1823  79  87   4 0.01
Thu 04/30 08Z 0.07 1722  83  92   4 0.01
Thu 04/30 09Z 0.09 1722  79  96   4 0.02
Thu 04/30 10Z 0.06 1621  88  96   4 0.05
Thu 04/30 11Z 0.03 1620  91  98   3 0.03
Thu 04/30 12Z 0.06 1717  92  99   2 0.01
Thu 04/30 13Z 0.06 1714  96  99   1 0.02
Thu 04/30 14Z 0.16 1913  98  99   1 0.03
Thu 04/30 15Z 0.25 2011  99  99   0 0.04
Thu 04/30 16Z 0.28 2209  99  89   0 0.03
Thu 04/30 17Z 0.34 2308  99  83   0 0.01
Thu 04/30 18Z 0.38 2607  98  85   0 0.00
Thu 04/30 19Z 0.43 3007  95  78   0 0.00
Thu 04/30 20Z 0.63 3108  94  69   0 0.00
Thu 04/30 21Z 0.28 3108  97  69   1 0.01
Thu 04/30 22Z 0.32 3113  98  64   0 0.03
Thu 04/30 23Z 0.31 3216  97  57   0 0.01
Fri 05/01 00Z 0.31 3217  96  59   0 0.01
Fri 05/01 01Z 0.34 3218  95  66  -1 0.01
Fri 05/01 02Z 0.36 3219  95  67  -1 0.00
Fri 05/01 03Z 0.37 3219  95  65  -2 0.00
Fri 05/01 04Z 0.36 3220  94  66  -2 0.01
Fri 05/01 05Z 0.40 3221  93  65  -2 0.01
Fri 05/01 06Z 0.39 3120  93  66  -3 0.00
Fri 05/01 07Z 0.38 3120  92  66  -3 0.00
Fri 05/01 08Z 0.38 3120  92  53  -3 0.00
Fri 05/01 09Z 0.39 3119  90  42  -3 0.00
Fri 05/01 10Z 0.37 3120  88  36  -3 0.00
Fri 05/01 11Z 0.36 3119  85  35  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.37 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