NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260831_0600
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)
=== ===== === ==== ==== === === === ====
Mon 08/31 06Z 0.05 3415  88   5  10 0.00
Mon 08/31 07Z 0.03 3514  85   3   9 0.00
Mon 08/31 08Z 0.03 3510  83   2   9 0.00
Mon 08/31 09Z 0.06 3309  80   0   9 0.00
Mon 08/31 10Z 0.10 3208  74   0  10 0.00
Mon 08/31 11Z 0.07 3308  65   0  10 0.00
Mon 08/31 12Z 0.06 3308  62   0  11 0.00
Mon 08/31 13Z 0.07 3307  62   0  10 0.00
Mon 08/31 14Z 0.08 3206  63   0  10 0.00
Mon 08/31 15Z 0.06 3204  62   1  10 0.00
Mon 08/31 16Z 0.08 3103  65   4  10 0.00
Mon 08/31 17Z 0.12 2702  70  12  10 0.00
Mon 08/31 18Z 0.42 2604  71  21  11 0.00
Mon 08/31 19Z 0.54 2504  65  36  11 0.00
Mon 08/31 20Z 0.48 2404  60  53  11 0.00
Mon 08/31 21Z 0.28 2503  60  60  12 0.00
Mon 08/31 22Z 0.16 2303  60  79  12 0.00
Mon 08/31 23Z 0.10 2202  64  86  12 0.00
Tue 09/01 00Z 0.13 2004  69  79  11 0.00
Tue 09/01 01Z 0.13 2004  74  68  11 0.00
Tue 09/01 02Z 0.12 2004  78  60  11 0.00
Tue 09/01 03Z 0.13 2004  83  59  11 0.00
Tue 09/01 04Z 0.10 2004  87  52  11 0.00
Tue 09/01 05Z 0.10 2103  90  52  11 0.00
Tue 09/01 06Z 0.09 2103  92  48  11 0.00
Tue 09/01 07Z 0.08 2103  92  53  11 0.00
Tue 09/01 08Z 0.02 1602  91  43  12 0.00
Tue 09/01 09Z 0.08 1304  91  33  12 0.00
Tue 09/01 10Z 0.10 1406  92  30  12 0.00
Tue 09/01 11Z 0.10 1409  93  29  12 0.00
Tue 09/01 12Z 0.09 1512  95  25  12 0.01
Tue 09/01 13Z 0.11 1514  96  39  12 0.01
Tue 09/01 14Z 0.11 1514  96  60  12 0.01
Tue 09/01 15Z 0.12 1515  96  77  12 0.01
Tue 09/01 16Z 0.10 1515  96  92  12 0.01
Tue 09/01 17Z 0.11 1516  97  97  13 0.04
Tue 09/01 18Z 0.13 1517  98  97  13 0.07
Tue 09/01 19Z 0.13 1518  96  95  13 0.10
Tue 09/01 20Z 0.14 1519  96  86  13 0.07
Tue 09/01 21Z 0.14 1519  97  82  13 0.03
Tue 09/01 22Z 0.11 1519  97  78  13 0.05
Tue 09/01 23Z 0.10 1517  97  64  13 0.03
Wed 09/02 00Z 0.05 1616  97  50  14 0.04
Wed 09/02 01Z 0.05 1714  97  52  14 0.03
Wed 09/02 02Z 0.04 1613  98  42  14 0.03
Wed 09/02 03Z 0.04 1614  98  36  14 0.03
Wed 09/02 04Z 0.04 1617  98  30  13 0.04
Wed 09/02 05Z 0.03 1618  98  24  13 0.02
Wed 09/02 06Z 0.04 1618  98  14  13 0.02
Wed 09/02 07Z 0.03 1618  98  12  12 0.02
Wed 09/02 08Z 0.04 1618  97  11  12 0.02
Wed 09/02 09Z 0.04 1618  98  12  12 0.01
Wed 09/02 10Z 0.03 1617  97  13  12 0.01
Wed 09/02 11Z 0.06 1616  97  13  12 0.01
Wed 09/02 12Z 0.03 1716  96  14  12 0.01
Wed 09/02 13Z 0.04 1614  95  15  12 0.01
Wed 09/02 14Z 0.04 1715  95  15  12 0.01
Wed 09/02 15Z 0.05 1714  96  22  12 0.01
Wed 09/02 16Z 0.03 1713  94  37  12 0.01
Wed 09/02 17Z 0.02 1713  89  47  13 0.00

Run total areal avg QPF for the Central_Greens is: 0.77 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