NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260918_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)
=== ===== === ==== ==== === === === ====
Fri 09/18 18Z 0.34 3315  91   1   8 0.00
Fri 09/18 19Z 0.72 3317  84   2   8 0.00
Fri 09/18 20Z 0.76 3318  77   1   7 0.00
Fri 09/18 21Z 0.61 3320  75   2   7 0.00
Fri 09/18 22Z 0.28 3322  68   2   7 0.00
Fri 09/18 23Z 0.19 3324  55   3   7 0.00
Sat 09/19 00Z 0.13 3424  51   4   6 0.00
Sat 09/19 01Z 0.06 3424  52   4   6 0.00
Sat 09/19 02Z 0.03 3524  56   4   6 0.00
Sat 09/19 03Z 0.07 3523  59   4   6 0.00
Sat 09/19 04Z 0.08 3520  56   4   6 0.00
Sat 09/19 05Z 0.09 0018  53   4   6 0.00
Sat 09/19 06Z 0.07 0016  51   3   6 0.00
Sat 09/19 07Z 0.04 3514  49   3   7 0.00
Sat 09/19 08Z 0.01 3514  45   3   7 0.00
Sat 09/19 09Z 0.01 3414  40   3   7 0.00
Sat 09/19 10Z 0.02 3514  35   3   8 0.00
Sat 09/19 11Z 0.03 3514  31   3   8 0.00
Sat 09/19 12Z 0.05 0014  30   3   8 0.00
Sat 09/19 13Z 0.06 0012  31   3   8 0.00
Sat 09/19 14Z 0.06 0009  33   4   7 0.00
Sat 09/19 15Z 0.07 0106  36   4   7 0.00
Sat 09/19 16Z 0.05 0104  41   4   6 0.00
Sat 09/19 17Z 0.05 0302  44   4   6 0.00
Sat 09/19 18Z 0.03 0001  47   4   6 0.00
Sat 09/19 19Z 0.03 0001  49   5   6 0.00
Sat 09/19 20Z 0.08 2301  54   5   6 0.00
Sat 09/19 21Z 0.05 1301  57   5   6 0.00
Sat 09/19 22Z 0.06 1902  58   6   6 0.00
Sat 09/19 23Z 0.05 1803  58   6   6 0.00
Sun 09/20 00Z 0.05 1805  52   6   7 0.00
Sun 09/20 01Z 0.06 1806  51   5   7 0.00
Sun 09/20 02Z 0.08 1808  49   5   7 0.00
Sun 09/20 03Z 0.08 1809  49   4   8 0.00
Sun 09/20 04Z 0.14 1912  51   5   7 0.00
Sun 09/20 05Z 0.18 1914  52   6   7 0.00
Sun 09/20 06Z 0.22 1916  48   7   7 0.00
Sun 09/20 07Z 0.28 2017  50   8   6 0.00
Sun 09/20 08Z 0.35 2018  63  11   6 0.00
Sun 09/20 09Z 0.31 2018  76  18   6 0.00
Sun 09/20 10Z 0.26 2018  80  26   6 0.00
Sun 09/20 11Z 0.26 2018  85  20   6 0.00
Sun 09/20 12Z 0.21 1917  87  25   6 0.00
Sun 09/20 13Z 0.15 1916  87  74   6 0.00
Sun 09/20 14Z 0.09 1815  90  98   6 0.00
Sun 09/20 15Z 0.03 1717  92  99   6 0.02
Sun 09/20 16Z 0.02 1719  90  99   6 0.04
Sun 09/20 17Z 0.03 1720  93  99   6 0.07
Sun 09/20 18Z 0.02 1719  97  99   7 0.13
Sun 09/20 19Z 0.03 1619  98  99   7 0.14
Sun 09/20 20Z 0.05 1620  98  99   7 0.15
Sun 09/20 21Z 0.06 1621  98  97   7 0.14
Sun 09/20 22Z 0.05 1621  97  95   8 0.13
Sun 09/20 23Z 0.06 1620  97  88   9 0.08
Mon 09/21 00Z 0.10 1518  98  93   9 0.06
Mon 09/21 01Z 0.13 1416  98  94   8 0.05
Mon 09/21 02Z 0.12 1413  98  94   8 0.04
Mon 09/21 03Z 0.14 1210  98  97   7 0.03
Mon 09/21 04Z 0.15 1008  98  85   7 0.02
Mon 09/21 05Z 0.13 0705  98  67   7 0.01

Run total areal avg QPF for the Central_Greens is: 1.11 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