NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260428_1800
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)
=== ===== === ==== ==== === === === ====
Tue 04/28 18Z 2.00 1512  55  11   7 0.00
Tue 04/28 19Z 1.89 1514  56  12   7 0.00
Tue 04/28 20Z 0.75 1614  57  17   7 0.00
Tue 04/28 21Z 0.51 1614  61  16   7 0.00
Tue 04/28 22Z 0.62 1516  64   6   6 0.00
Tue 04/28 23Z 0.44 1519  68   3   5 0.00
Wed 04/29 00Z 0.28 1522  72  20   5 0.00
Wed 04/29 01Z 0.11 1623  71  58   5 0.00
Wed 04/29 02Z 0.05 1621  66  78   5 0.00
Wed 04/29 03Z 0.09 1721  64  87   5 0.00
Wed 04/29 04Z 0.20 1821  68  84   4 0.00
Wed 04/29 05Z 0.23 1919  73  77   4 0.00
Wed 04/29 06Z 0.25 1918  70  78   4 0.00
Wed 04/29 07Z 0.25 2017  69  78   4 0.00
Wed 04/29 08Z 0.25 2017  67  65   4 0.00
Wed 04/29 09Z 0.17 2014  64  51   6 0.00
Wed 04/29 10Z 0.18 2014  67  48   6 0.00
Wed 04/29 11Z 0.23 2114  72  47   6 0.00
Wed 04/29 12Z 0.20 2112  78  40   6 0.00
Wed 04/29 13Z 0.11 2008  79  31   7 0.00
Wed 04/29 14Z 0.07 1907  79  31   7 0.00
Wed 04/29 15Z 0.10 1908  81  36   6 0.00
Wed 04/29 16Z 0.10 1607  81  32   6 0.00
Wed 04/29 17Z 0.19 1608  80  38   6 0.00
Wed 04/29 18Z 0.76 1509  77  39   6 0.00
Wed 04/29 19Z 1.66 1511  76  42   6 0.00
Wed 04/29 20Z 1.81 1511  75  51   6 0.00
Wed 04/29 21Z 1.86 1512  75  52   6 0.00
Wed 04/29 22Z 2.19 1414  77  45   6 0.00
Wed 04/29 23Z 0.36 1515  80  42   6 0.00
Thu 04/30 00Z 0.16 1517  87  39   7 0.00
Thu 04/30 01Z 0.11 1519  83  40   7 0.00
Thu 04/30 02Z 0.09 1520  77  43   7 0.00
Thu 04/30 03Z 0.07 1622  73  47   7 0.00
Thu 04/30 04Z 0.08 1623  72  49   7 0.00
Thu 04/30 05Z 0.09 1525  81  57   7 0.01
Thu 04/30 06Z 0.09 1525  91  68   7 0.01
Thu 04/30 07Z 0.11 1526  94  73   7 0.01
Thu 04/30 08Z 0.16 1527  95  55   7 0.01
Thu 04/30 09Z 0.13 1527  96  74   7 0.02
Thu 04/30 10Z 0.09 1526  98  89   6 0.04
Thu 04/30 11Z 0.03 1623  98  95   5 0.07
Thu 04/30 12Z 0.04 1717  98  93   5 0.07
Thu 04/30 13Z 0.04 1614  98  97   3 0.09
Thu 04/30 14Z 0.04 1612  98  99   3 0.05
Thu 04/30 15Z 0.04 1708  99  96   2 0.03
Thu 04/30 16Z 0.06 1805  99  96   1 0.02
Thu 04/30 17Z 0.12 2105  99  99   1 0.04
Thu 04/30 18Z 0.24 2506  99  98   1 0.03
Thu 04/30 19Z 0.33 2708  99  97   0 0.03
Thu 04/30 20Z 0.45 2912  99  97   0 0.03
Thu 04/30 21Z 0.43 3015  98  95   0 0.02
Thu 04/30 22Z 0.40 3117  97  93   0 0.01
Thu 04/30 23Z 0.46 3017  97  94  -1 0.02
Fri 05/01 00Z 0.46 3018  97  90  -2 0.01
Fri 05/01 01Z 0.51 3020  97  79  -2 0.01
Fri 05/01 02Z 0.56 3020  96  63  -3 0.01
Fri 05/01 03Z 0.59 3021  96  48  -3 0.01
Fri 05/01 04Z 0.60 3021  95  44  -4 0.00
Fri 05/01 05Z 0.55 3021  95  43  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.65 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